41 replies to this topic

[dskippy]

Hello everyone, and in particular Doom (btrettel)

 

I'm interested in making a pneumatic semi-auto similar to Doom's FANG. I've created a 3D printed part that mates with the standard Nerf-band clip that I'm pretty happen with. I just need to figure out which air cylinder I'll be using to feed the darts through.

 

I'm hoping to get exact specs or part numbers on the air cylinder that was used on FANG upgrades. I've done some reading on the original FANG post here.

 

http://nerfhaven.com...un-prototype-1/

 

It was found in the parts bin so he didn't have a part number. He also said this: 

 

After some discussion at Spudfiles, I've already decided on one major change from prototype 1 to 2. I used a spring-return air cylinder here. The air cylinder seems to be designed to move the rod at once rather than gradually, so the spring is prestressed. To keep the force increase small, the spring doesn't travel much and has a low spring constant. And to keep the force sufficiently high to return, the spring must be rather long. All that combines to make a long air cylinder. My cylinder was about 8 or 9 inches long when it only had a 4 inch stroke.

The solution is to use a dual action air cylinder and make one side contain compressed air, with a small air chamber attached to the opening. This will still allow the spring to return all at once, but the energy can be stored in a dimension other than length.

 

So simply put, what have people had the most success with? The task is pretty simple but buying several air cylinders and using trial and error could be pretty expensive.

 

Based on my measurements and Doom's being 4" I'm tentatively looking at the smallest and cheapest McMaster-Carr air cylinder with a 4" stroke. 6498K114 with a or 6498K516 which is 3/4" longer.

 

Does anyone have any opinions on these? Does anyone have any experience with others that they recommend or would suggest avoiding? Does anyone use regulators to restrict airflow to slow down the movement of the cylinder? I've considered doing that but I haven't had my hands on one yet so I don't know if the speed will be too fast anyway.

 

Thanks for the help. One I get enough into on this thread to make a decision I'll put together a test and get my 3D printed part and McMaster-Carr parts list up here on Nerf Haven. 

[Ice Nine]

I hesitate to speak for Doom, but my understand is that he's pretty busy with work and research at the moment. You might have the best luck reaching out to him via email; I believe that his email is listed in his signature. He could probably tell you exactly which cylinder he used.

 

You might also consider that you probably don't need a four-inch stroke for the breech, unless you're using stock darts, and maybe not even then. I admit that I'm not familiar at all with the air cylinders that McMaster offers beyond discussing them with Doom as I was working out ideas for a project.

 

Does your project require stock darts? If it does, and you have access to a 3D printer, you may have better luck printing a low-angle long wye that can feed stock darts, since these pneumatic blasters can be scaled to match pretty much any power needs to cover for per-round inefficiency. I understand the benefits of the N-Strike clip system, but the increased complexity is a pretty steep price to pay, especially if a breech system eats a dart (e.g. Slug's ABP5K, which might be a good reference for your system).

 

On reflection, Slug's design is much more complicated than the FANG and probably not a great place to look for air cylinder/breech inspiration, but I'll leave it in because it's a fun read.

Edited by Ice Nine, 01 December 2015 - 03:29 PM.

[dskippy]

Yes, I'll probably email Doom directly at some point. I wanted to start up a thread for the community first to see what everyone else has had success with and record it for posterity. If Doom doesn't chime in though, perhaps I'll email and just ask which specific cylinders he's had the most luck with.

 

As for my project, I am pretty set on using stock darts and stock clips. For starters, I like using stock darts because they are interchangeable with the ammo of my arch nemesis (nephew) and I can thus return fire sent my way. Also I'm not really into making darts. The standard clips are just boxes with springs that work perfectly well too so I don't think I can do any better than nerf has ever done on that front. So yeah, for this project, I'm using all stock darts and clips. 

 

I measure the stock dart and clip and found that in required something just shy of 4" to make the trip through the clip. 4" might be more than I need, but not by much.

 

I've read Slugs page too, in researching this project. Definitely a good read. Oddly enough he also does not mention which off-the-shelf air cylinder he used.

[The2ndBluesBro]

Check out Slug's ARR as well. It's in the homemades directory. 

[dskippy]

Check out Slug's ARR as well. It's in the homemades directory. 

 

Yeah I did already. He machines his own. I'm hoping to just buy this part.

[shmmee]

I'm having a tough time accessing my photobucket account, but I've got a video of a (Failed) attempt at a piston breech loader I tried. It loaded darts well, but it failed to seal well enough to fire it. The concept was extremely simple. I'm hoping it'll give you another option to work with. It could be modified to shoot stock darts by substituting a longer piston with more travel (About 3.5" worth) I'd suggest one with a 3/8" or 1/2" bore for this project. Any bigger and you'd be using a ton of air since the piston is acting as a tank expansion, and the increased force from the larger diameter could break your build.

 

I used a back pressure style tank (hornet, panther, big salvo...) and gooped a hose from the side of the tank to a piston. I chopped a mag well in a piece of sch 80, and tee'd the tank in crossways just in front of the magwell and used the piston to advance a pusher rod (a 1/2" wood dowel) that fed a dart from a mag forward into the breech. When the tank filled, the piston extended and it pushed a dart forwards into the breech. When the tank fired (depressurized) the piston also depressurized through the tank and a rubber band pulled the piston backwards retracting the pusher and allowing the next dart to come up from the mag.  It didn't require any action beyond filling and firing the airtank and with a mavo-3 3way valve the system became semi auto. It just didn't seal well enough to shoot more than a few feet. Proof of concept achieved though.

 

I should of used a real piston with more travel instead of substituting a secret shot 2 pump for the piston. It didn't have enough travel to load the dart (slug) and seal the breech. Solve that seal issue and you'd be set. 3D printing the breech would of helped too since it would of been easier to design in a conical receiver in front of the mag for the pusher to seal against.

 

I'll try to edit this post with a link to the video once i'm on a more friendly computer. I've shared it to NH before, but I really doubt you'll want to go through all my posts to find it... Hopefully it'll provide you with some inspiration to work with. 

 

... I tried uploading it but appearantly " you aren't permitted to upload this kind of file". It's an MP4 video. Admin thoughts?

 

... I wandered back through my posts and found it. I hope the link works, and that it's the right video. I can't verify it from this computer...

 

http://vid1107.photo...to/DSCN1997.mp4

Edited by shmmee, 02 December 2015 - 04:51 PM.

[dskippy]

This is great, thanks for finding the video. You did something similar to what Doom seems to be convinced he wanted to do. Which was to use an external extension spring (in your case, rubber band) to return the piston. This reduces the length that the cylinder need to be in order to have a 4" stroke. It's a rather interesting idea, I must say. It does require a decent amount of extra work in some designs to accomplish this though. It really depends on whether you can handle the cylinder being 10" long instead of 6" long.

 

Your design's problem was not sealing properly. Do you know if it ever seals or if the seal pulls apart too quickly? What problem I have with the design is that intuition tells me that if firing the gun pulls the seal back out of the back of the barrel, you are likely to never have a sealed barrel while firing. This is solved if the seal slides into the barrel so far that it doesn't escape until the dart is out of the barrel. So I'm wondering, how much overlap do you need? It of course depends on how fast your cylinder empties. One could place a flow restricter on the connection between the blast chamber and the cylinder to ensure that this goes pretty slowly.

 

Does your model pull out too quickly and thus destroy the seal it created or did it never really move far enough forward to seal?

 

Thanks again for posting your video. Where did you get that piston?

[shmmee]

The model in the video was only meant to be a proof of concept prototype, one which I never managed to revisit and improve upon sadly. As such I wasn't looking for a perfect seal, or even a decent one. With the piston extended in the sealed position (I harvested a pump from a secret shot II from my parts bin for my piston) I could blow on the end of the barrel and feel a steady stream of air rushing out of the breech with very little resistance building. The piston on my prototype didn't travel far enough forward to completely move past the breech, which leaked horribly. Darts fell out of the barrel with the enthusiasm of a geriatric sloth.

 

The breech only needs to seal for as long as the dart is in the barrel. Bracing the piston forward and range testing or chrony-ing a few shots would give a good baseline of what the blaster should be doing. If the breech opens prematurely range/dart speed will drop significantly.

 

Choking off the air line to the piston was something I was planning on exploring in a later model - to see if it was even need at all. If it was needed I was going to tee the tubing to the piston and add check valves to create a dedicated fill and return air line - and choke off the return air line. (fast fill, slowed emptying)  Choking off the return line was something i was hoping to avoid. Plumbing the tank to the piston added the bonus of making the piston into an expanded air tank. If pressure is slowed it would of negated that and any air in the piston would of been wasted. Since you're planning on utilizing a 3d printer, it should also be possible to engineer a longer sealed section between the tank and the mag well so the piston can begin it's return travel and still remain sealed. It would be adding dead space as the piston retracted, but at least the air in the piston would be feeding back into the tank and out to the barrel at it's fullest velocity.  I'd guess it wouldn't take more than a quarter inch or two of seal to give the dart enough time to exit the barrel, but that's yet to be proven.

 

I also remember learning that they make pistons with an internal spring to automatically retract the piston once it looses air pressure. That would be worth looking into, that way you can ditch the rubber band return spring and place the piston directly behind the mag well. You would still need to use a pusher rod so the following dart can't hop up and get caught behind the piston head once the piston pushes past to load a dart though. Ditching the home brew rubber band for a piston internal return spring would also make one less thing to go wrong. Since you're planning on using stock darts, I'd suggest looking for a piston with 4" to 4 1/2" of travel. That should give you your 3" for the dart and another inch or so to play with in seal and return clearances.

 

It's also worth noting that even an efficient semi auto system with a small tank will use a ton of air. I used a clippard mavo-3 3way valve to make a semi auto dart tag gun with a bike innertube reinforced RF20 bladder (I think I got it up to about 45 psi) and a panther tank. Tons of pumping to fill the bladder and I could only get 8 of the 10 shots off. It was tough keeping that turret fed as well. It was an awesome blaster, but it's combined hunger for air and individually loaded darts made it tough to manage in an open field war. It would of been a little easier if it had been a clip fed system like you're working towards, but it'll still be a ton of pumping air. 

 

So, what are you planning on doing for air? Bladder, small hand filled hard tank/regulator , large compressor filled hard tank/regulator, single shot pump to prime?

Edited by shmmee, 03 December 2015 - 11:55 AM.

[Meaker VI]

As for my project, I am pretty set on using stock darts and stock clips. For starters, I like using stock darts because they are interchangeable with the ammo of my arch nemesis (nephew) and I can thus return fire sent my way. Also I'm not really into making darts. The standard clips are just boxes with springs that work perfectly well too so I don't think I can do any better than nerf has ever done on that front. So yeah, for this project, I'm using all stock darts and clips.

 

I see that you'd prefer to use stock darts and clips, but have you considered doing a (much easier) QEV Airgun by Ice Nine (who is posting RIGHT HERE, so you can easily ask him questions directly) instead? You can use an RSCB or as Ice says, a low-angle custom Y for stock darts, and you won't need all the complex (and jam prone) clip parts. You can even use an RSCB as a clip by swapping out the 1/2" PVC tube-mag.

 

A semi-auto breech-loaded compressed air NERF gun is still a kind of bleeding-edge blaster. NERF doesn't make one, only a few scattered homemade prototypes exist built by our top designers, and even very well built they'll still be prone to jamming. If you build one it'll be awesome, but it's a lot more work than is necessary to be very competitive.

[dskippy]

I see that you'd prefer to use stock darts and clips, but have you considered doing a (much easier) QEV Airgun by Ice Nine (who is posting RIGHT HERE, so you can easily ask him questions directly) instead? You can use an RSCB or as Ice says, a low-angle custom Y for stock darts, and you won't need all the complex (and jam prone) clip parts. You can even use an RSCB as a clip by swapping out the 1/2" PVC tube-mag.

 

A semi-auto breech-loaded compressed air NERF gun is still a kind of bleeding-edge blaster. NERF doesn't make one, only a few scattered homemade prototypes exist built by our top designers, and even very well built they'll still be prone to jamming. If you build one it'll be awesome,but it's a lot more work than is necessary to be very competitive.

 

No sorry, I'm not interested. I have already built stuff like that. The fact that the air cylinder design is bleeding edge is exactly why I'm interested. And I'm not trying to be competitive in nerf wars. I'm trying to impress my nephew with cool stuff. I'm also trying to challenge myself to make something new and different and potentially contribute to the body of knowledge of the community. So, yeah, hoppers and RSCBs are out. I have a bunch of them.

[dskippy]

Since you're planning on utilizing a 3d printer, it should also be possible to engineer a longer sealed section between the tank and the mag well so the piston can begin it's return travel and still remain sealed. It would be adding dead space as the piston retracted, but at least the air in the piston would be feeding back into the tank and out to the barrel at it's fullest velocity.  I'd guess it wouldn't take more than a quarter inch or two of seal to give the dart enough time to exit the barrel, but that's yet to be proven.

 

I'd suggest looking for a piston with 4" to 4 1/2" of travel. That should give you your 3" for the dart and another inch or so to play with in seal and return clearances.

 

It's also worth noting that even an efficient semi auto system with a small tank will use a ton of air. 

 

So, what are you planning on doing for air? Bladder, small hand filled hard tank/regulator , large compressor filled hard tank/regulator, single shot pump to prime?

 

This is why I plan to do based off this discussion and also what I've seen from Doom and Captain Slug's work. As for the tank, it'll be a modular quick connect that I'll connect to a few different things, I imagine. Primarily will be a large, high-pressure tank with a regulator. I might get a paintball tank + regulator and have it filled so that I can actually have a decent amount of air life time. However I also plan to make a backpack sized 100psi tank that I can clamp a bike pump to and pump up myself. The tanks will be connected via hose to a quick connect on the back of the gun, which of course has its own, must smaller, blast chamber on it and will operate and about 30-40psi with a controlled volume. Pretty standard for this kind of blaster, really.

 

Also, after doing a lot of reading on the forums. This one a SpudFiles I've actually ordered an air cylinder.

 

I didn't order a single-acting, spring return cylinder like you suggested. Doom came to the conclusion that he wanted to switch from his existing single-acting to a double acting because the single acting was really long and bulky. The double acting requires that you create your own return mechanism, so I was pretty torn on which to go with. But I ultimately went with the double. I am considering using an air spring for the return. It's hard to buy air springs that are small enough though. Most of them are meant for car suspension. If anyone knows a good solution let me know. I am considering just filling one side of the piston with some low pressure and seeing if that works for me. Otherwise, I might end up using an external spring attached to the mechanism that the piston is moving to return it.

 

Another decision I need to make now is whether to push the dart into the back of the barrel or if I want to pull the barrel back over the dart. Pull seems to have less dead space and makes machining the blast hole must simpler. Pushing seems to be less prone to jamming.

[shmmee]

 

This is why I plan to do based off this discussion and also what I've seen from Doom and Captain Slug's work. As for the tank, it'll be a modular quick connect that I'll connect to a few different things, I imagine. Primarily will be a large, high-pressure tank with a regulator. I might get a paintball tank + regulator and have it filled so that I can actually have a decent amount of air life time. However I also plan to make a backpack sized 100psi tank that I can clamp a bike pump to and pump up myself. The tanks will be connected via hose to a quick connect on the back of the gun, which of course has its own, must smaller, blast chamber on it and will operate and about 30-40psi with a controlled volume. Pretty standard for this kind of blaster, really.

 

Also, after doing a lot of reading on the forums. This one a SpudFiles I've actually ordered an air cylinder.

 

I didn't order a single-acting, spring return cylinder like you suggested. Doom came to the conclusion that he wanted to switch from his existing single-acting to a double acting because the single acting was really long and bulky. The double acting requires that you create your own return mechanism, so I was pretty torn on which to go with. But I ultimately went with the double. I am considering using an air spring for the return. It's hard to buy air springs that are small enough though. Most of them are meant for car suspension. If anyone knows a good solution let me know. I am considering just filling one side of the piston with some low pressure and seeing if that works for me. Otherwise, I might end up using an external spring attached to the mechanism that the piston is moving to return it.

 

Another decision I need to make now is whether to push the dart into the back of the barrel or if I want to pull the barrel back over the dart. Pull seems to have less dead space and makes machining the blast hole must simpler. Pushing seems to be less prone to jamming.

I've never researched air springs before, but i'm guessing they're just chambers you can pressurize slightly to supply a counter pneumatic force, right? That would be a low psi thing, I bet you could build your own out of pvc. Just goop a stem into a drilled hole and you can give it a little pressure to return the piston and then detach the pump. An air spring is a really good idea. I'll have to remember that.

 

Nerf favors a stationary dart and a retracting bolt slead. It's harder to get them to seal, but that may be more reliable with less modification. You could just attach the piston directly to an existing bolt slead. Poof done. I'm remembering a bolt sled seal but can't remember the name. I know it's not an angel breach... i think it might of been called a Rev breach? they used a petg tube inserted into the bolt sled and it would slide back and seal around an 11/32" brass tube nub. It might of been on the old and departed Nerfrevolution site though. It'd be worth looking into.

[rego]

If I remember correctly, I recall reading a thread on spudfiles that simply capping off the return port of the cylinder with a plug worked perfectly. I would recommend to try out that route first, being the smallest, cheapest, and easiest. Otherwise the next easiest would be to use normal extension springs between the frame of the blaster and ram (the moving part). 

 

I would also recommend reading through all of captainslug's abp5k and arr threads. While most of it is not particularly useful, the design of the arr seems like it would help with component placement. He placed the qev in front of the breech and entered the barrel at 90 degrees, which keeps deadspace limited. The bolt is solid and rams darts in front of the qev port in the barrel.

 

This can also be seen in pvcarsenal17's RR Assisted Bolt action. Almost no information about it, but spudfiles has the thread with pictures and short descriptions. It seems similar to this, with almost entirely off the shelf parts

[dskippy]

rego,

 

Thanks. I have extensively read Captain Slug's stuff and it's all great. Especially the ARB5K. I'm basically trying to make that gun for myself with two difference.

 

Primarily, I want to 3D print the clip retainer and breach. I think I can get much more reliable loading out of a 3D printed part that fits the stock elite clips perfectly and pushes the bolt sled or brass tube into exactly the right place. Rather than sawing brass tube and hanging it at the right height above it the clip and trying to hot glue some bs onto it to push the dart down the right way. It's finicky enough that I think if I put enough design into it now, I can 3D print something that a lot people can use in future designs.

 

Secondly I'm just going to use off-the-shelf DCV and QEV combo rather than machining my own valve. His is badass and I might copy that design one day but not on this build.

 

Rego you seem to be advocating for pushing the dart in from the back of the clip into the barrel and feeding air in 90 degrees (likely from the bottom) which is one design I'm debating. The other is the one that shmmee pushed for in his post just above yours, which slides the barrel over the dart and seals to the back of the clip chamber where the air comes in. Do you have any reasons for choosing one or the other? Any information is helpful. I really don't know what I'm going to do on that front.

 

As for using a double acting cylinder and an air spring, I do intend to try what you suggested. I was going to pump air in the back and leave an intake valve on it. I actually hadn't considered that just plain old sealing it (while the piston is fully extended) might actually be enough. That's pretty cool and I'll try that as soon as it comes in a couple of days.

 

For the record I ordered McMaster-Carr part #6498K849

[jwasko]

Reading through the thread, I was going to post the same recommendation that Rego did, minus the link to prior work.

 

In some of my experience using N-strike clips with a brass breech, I've found that it is more reliable to simply push the dart out of the clip using a "ram" and into a semi-loose tube a "chamber" rather than to have it enclosed by two thin-walled tubes like in a brass-breeched longshot. The knife edge of the brass tends to cut into either the dart to be loaded, or the next dart down.

 

Now, there are people who make brass-breeched longshots who say they feed very reliably. So it can be done, but many people find it difficult to achieve.

 

On the other hand, I've made a ram by putting a conical tip (made out of wood, but you could use plastic) onto a piece of brass. The conical tip pushes the dart ahead of the ram and into the chamber while avoiding pinching either the dart to be loaded or the next dart. Then, the cylindrical portion of the ram continues forward as far as needed to seal with the chamber.

 

Side note to everyone besides the OP that thinks he should use a hopper: Personally, I think this design would be even more reliable than a hopper, but I have yet to war-test the design in order to prove the theory. I'm anti-hopper, though, so it may be personal prejudice that's influencing my opinion.

 

Now the problem with the ram is that it adds a lot of dead space between the dart and the firing valve...unless you release the air into the chamber perpendicular to the barrel.

 

The conical portion of the ram should coincidentally help the air flow get from the perpendicular valve to the back of the dart, but you could also alter the design of the ram to something like how Buzz Bee's Rapid Fire Rifle was made (cut a hole into the side of the ram and channel the air into the ram then out the front of the cone).

 

Edit: On second though, the Rapid Fire Rifle design would just worsen the (possible) need to delay retraction of the piston, given that the hole in the ram would need to stay lined up in order to allow air flow.

 

PS: The price of that cylinder is painful.

 

Edit 2: Alternative cylinder???? http://www.ebay.com/...50AAOxy-sRSYkiG

Edited by jwasko, 04 December 2015 - 04:33 PM.

[Meaker VI]

Primarily, I want to 3D print the clip retainer and breach. I think I can get much more reliable loading out of a 3D printed part that fits the stock elite clips perfectly and pushes the bolt sled or brass tube into exactly the right place. Rather than sawing brass tube and hanging it at the right height above it the clip and trying to hot glue some bs onto it to push the dart down the right way. It's finicky enough that I think if I put enough design into it now, I can 3D print something that a lot people can use in future designs.

 
Emphasis mine. I'd be a bit leery of 3d printing the breach. By all means, 3d print all the complex parts of it (the magwell, any moving parts), but the operable, sealing, breech parts that hold the darts should be purchased from standard stock.
 
I may be misreading you and that's exactly in line with what you're doing.
 

In some of my experience using N-strike clips with a brass breech, I've found that it is more reliable to simply push the dart out of the clip using a "ram" and into a semi-loose tube a "chamber" rather than to have it enclosed by two thin-walled tubes like in a brass-breeched longshot. The knife edge of the brass tends to cut into either the dart to be loaded, or the next dart down.
 
...
 
 
On the other hand, I've made a ram by putting a conical tip (made out of wood, but you could use plastic) onto a piece of brass. The conical tip pushes the dart ahead of the ram and into the chamber while avoiding pinching either the dart to be loaded or the next dart. Then, the cylindrical portion of the ram continues forward as far as needed to seal with the chamber.

 
The "push dart into chamber" method should work very well IF:
A ) The dart is sufficiently supported so it doesn't bend or
B ) The chamber is sufficiently loose so the dart doesn't meet enough resistance to cause it to bend.
 
I think the dart-bending issue alongside their desire to use very short barrels led NERF to go with the more complex dart-tooth system they use than some of the seemingly simple breech-style solutions we use. The chamber could be (should be!) chamfered like the entrance to an RSCB and over sized a bit so the darts have wiggle room, trading efficiency for reliability.
 

Side note to everyone besides the OP that thinks he should use a hopper: Personally, I think this design would be even more reliable than a hopper, but I have yet to war-test the design in order to prove the theory. I'm anti-hopper, though, so it may be personal prejudice that's influencing my opinion.

I've never heard of or used anything nearly as reliable as a hopper/RSCB other than singling something. There are no moving parts to fail, nothing can jam, no parts prone to user-error failure. The instances where it fails to load are consistent and fairly easily identified by testing, especially compared to the instances where a clip system fails. It is a very elegant system - that looks stupid. So I'm anti hopper as well, and try to use RSCB's instead, at least they are more streamlined and not sticking way outside the blaster.

 

I've got a non-hopper/RSCB system I've tinkered slightly with and have been mentally toying with that should be as reliable (More, maybe) but is almost as mechanically complex as a clip and so haven't had the time or wherewithal to make it (basically, go back to a real clip where every dart is retained in a little barrel a fixed distance apart). And then I found BOOMco and so far, that's been killing my desire to pursue it. BOOMco clips achieve what I wanted to achieve without the hassle of me making anything (and probably cheaper than I could make them - I've been seeing ~$4 per clip & 20 darts online).

Edited by Meaker VI, 04 December 2015 - 05:26 PM.

[dskippy]

Emphasis mine. I'd be a bit leery of 3d printing the breach. By all means, 3d print all the complex parts of it (the magwell, any moving parts), but the operable, sealing, breech parts that hold the darts should be purchased from standard stock.
 
I may be misreading you and that's exactly in line with what you're doing.

 

Yes exactly. I'm not sure I'd say you're misreading me so much as I'd suspect I'm using the word breach inappropriately but yes that's my plan.

 

I will be 3D printing the magwell I guess it's called. It will hold the magazine in place as well as provide a connection on the back side for the air cylinder to firmly and reliably be placed exactly where it needs to be and also hold the barrel in place on the front. The 3D printed piece will also be responsible for having a cone in front for the dart to be guided into. So basically the 3D printed magwell will be for any fine tuned shaping that needs to be right in order for the darts not to jam, but will not be doing any air tight sealing.

 

Based on this thread I think I've decided to do push the dart in from the back of the magwell into the barrel rather than move the barrel back over the dart. I will be loading the dart into a barrel that has a QEV mounted at 90 degrees feeding air in from the bottom. I could potentially achieve this with a simple 1/2" PVC tee-joint. It would be press fit on the barrel and inlet side with a threaded female connection to the QEV on the bottom. The 1/2" PVC tee-joint might be quite a bit too large and have too much empty space for the dart to move around in though. If that's the case I might machine something out of a Derlin rod.

 

Also, just a quick note to anyone discussing hoppers. That is definitely not what this thread is about. I'm not going to use a hopper for this project even if it's better. This is about making a magazine fed pneumatic with an air cylinder. We can discuss the differences between them in another thread if you'd like.

Edited by dskippy, 06 December 2015 - 12:54 PM.

[Ice Nine]

Using a tee is probably a good plan. You might consider boring out the stoppers for 1/2" PVC in the "upper" part of the T-shape so 1/2" PVC can pass through. That way, you can put bore holes in the PVC and your barrel material to direct air onto the dart, and that way you wouldn't have to worry about seating the dart because it would never leave the barrel material.

 

Also, just a quick note to anyone discussing hoppers. That is definitely not what this thread is about. I'm not going to use a hopper for this project even if it's better. This is about making a magazine fed pneumatic with an air cylinder. We can discuss the differences between them in another thread if you'd like.

 

Even though it's your thread, it's not your place to dictate the discussion that takes place. Both Meaker and JWasko gave you significant contributions and their conversation was an aside. If someone started posting solely about hoppers, or to argue, then maybe you could step in.

 

(They are better, though.)

[jwasko]

The "push dart into chamber" method should work very well IF:
A ) The dart is sufficiently supported so it doesn't bend or
B ) The chamber is sufficiently loose so the dart doesn't meet enough resistance to cause it to bend.

Yes, this. I am thinking of not only a chamfer, but basically a one-dart-long RSCB clip (that is, an oversized tube that does not create an air-tight seal on the dart) that is reloaded after every shot. At the front of this RSCB/chamber would be your chamfer that seals around the very tip of the dart (again, like an RSCB). Depending on the location of the air outlet into the chamber, the oversized chamber would only facilitate airflow to the back of the dart, allowing the dart to be pushed out of the barrel.

I made a ~3-dart-long RSCB like this a while ago by modifying Zorn's n-strike breech. I think I used 19/32 brass as the chamber/RSCB clip, which also functions to support and guide the dart as you mention in A). A 9/16" brass ram was then created. The ram was manually operated, and never jammed on me in spite of the fact that the N-strike mag was held in solely by snapping the feed lips over the 19/32" brass half-pipe. If I knew where it was at the moment, I would simply post pictures and/or a video.
 

 

It is a very elegant system - that looks stupid.

True, this is one of my reasons for not wanting to use a hopper over an RSCB. Combined with somewhat less reliability in hoppers (observed on others' blasters) compared to RSCBs, I see no reason to use a hopper.

On the other hand, something mag-fed as we are discussing here could somewhat improve dart capacity compared to RSCBs while simultaneously reducing blaster length. Plus, it's just cool to tinker with...I've always loved the idea of an internal box magazine in nerf, and the Magnus only increased my interest.

[Meaker VI]

I will be 3D printing the magwell I guess it's called. It will hold the magazine in place as well as provide a connection on the back side for the air cylinder to firmly and reliably be placed exactly where it needs to be and also hold the barrel in place on the front. The 3D printed piece will also be responsible for having a cone in front for the dart to be guided into. So basically the 3D printed magwell will be for any fine tuned shaping that needs to be right in order for the darts not to jam, but will not be doing any air tight sealing.
 
Based on this thread I think I've decided to do push the dart in from the back of the magwell into the barrel rather than move the barrel back over the dart. I will be loading the dart into a barrel that has a QEV mounted at 90 degrees feeding air in from the bottom. I could potentially achieve this with a simple 1/2" PVC tee-joint.

Yes, this. I am thinking of not only a chamfer, but basically a one-dart-long RSCB clip (that is, an oversized tube that does not create an air-tight seal on the dart) that is reloaded after every shot. At the front of this RSCB/chamber would be your chamfer that seals around the very tip of the dart (again, like an RSCB). Depending on the location of the air outlet into the chamber, the oversized chamber would only facilitate airflow to the back of the dart, allowing the dart to be pushed out of the barrel.

Jwasko's got your solution dskippy - the 1/2" PVC T should be basically the right size for a 1-dart clip. Putting the 1/2" straight through it as Ice said would improve the system. Set your 3d printed part up as a female connection for the PVC T so you can just plug it in. I'd chamfer the 3d printed part, but just to soften the edges; the 1/2" PVC chamber might even stick through the wall of the 3d printed magwell. Here, it' easier to show than explain:

 

(So we're clear - 1/2" CPVC is what I'm showing as a barrel, but it's intened to be just whatever you'd use for a barrel. CPVC is a sadly pain to use for barrel material - it works great IF you can find exactly the right CPVC pipe that fits the darts well. If not, it doesn't work at all. I'm now a fan of the McMaster PETG, I think it's this number 2044T43. FYI - shipping is like $20 for that long stick, so buy a bunch or buy shorter lengths if you use it)

PVC is super easy to chamfer, and will feed better than the 3d printed part. Just stick it through and chamfer it; only really worrying about chamfering the 3d printed magwell if it is between the dart and the PVC for some reason.

Which may be likely - the bolt (part that pushes the dart into the chamber) should lock to keep it jumping when the blaster is fired. Look at Boltsniper's SCAR-N:

 

Since you're feeding air elsewhere and aren't using shells, your part probably doesn't need to be as complex. I'd just make the crazy lock shape a part of the magwell wall somewhere, possibly behind the mag (the unlabeled space on the right of my drawing). That'd also let you use a machined/maufactured part to seal with, while still 3d printing all the complex bits.

Edited by Meaker VI, 07 December 2015 - 10:48 AM.

[jwasko]

I should have you illustrate all my ideas, Meaker.

 

I wouldn't bother reaming out the T for a solid piece ov PVC, though...just use two stubs of PVC, with a piece of slightly smaller, thin-walled tubing in between (brass would be simplest, but not necessarily the best or cheapest solution).

 

Not sure how that interlocking bit would play with my tapered ram idea, but the telescoping design of the Scar-N breach could be used in case the ram retracts so quickly that the chamber seal is broken before the dart leaves the barrel. Rather than slowing the piston, just lengthen the dwell time of whatever part is doing the sealing.

Edited by jwasko, 07 December 2015 - 02:47 PM.

[Meaker VI]

I wouldn't bother reaming out the T for a solid piece ov PVC, though...just use two stubs of PVC, with a piece of slightly smaller, thin-walled tubing in between (brass would be simplest, but not necessarily the best or cheapest solution).

Agree - for simplicity, 2 pieces of PVC would be easier and faster.
 

Not sure how that interlocking bit would play with my tapered ram idea, but the telescoping design of the Scar-N breach could be used in case the ram retracts so quickly that the chamber seal is broken before the dart leaves the barrel. Rather than slowing the piston, just lengthen the dwell time of whatever part is doing the sealing.

The thing that a longer draw doesn't solve is 'bounce' in the breech caused by your pressure system charging the chamber suddenly- you'd loose efficiency. I think that Boltsniper talked about that while developing the SCAR-N as a result of observing it happen in the FAR. It also means you've got a longer blaster.

[dskippy]

Yes, this. I am thinking of not only a chamfer, but basically a one-dart-long RSCB clip (that is, an oversized tube that does not create an air-tight seal on the dart) that is reloaded after every shot. At the front of this RSCB/chamber would be your chamfer that seals around the very tip of the dart (again, like an RSCB). Depending on the location of the air outlet into the chamber, the oversized chamber would only facilitate airflow to the back of the dart, allowing the dart to be pushed out of the barrel.

I made a ~3-dart-long RSCB like this a while ago by modifying Zorn's n-strike breech. I think I used 19/32 brass as the chamber/RSCB clip, which also functions to support and guide the dart as you mention in A). A 9/16" brass ram was then created. The ram was manually operated, and never jammed on me in spite of the fact that the N-strike mag was held in solely by snapping the feed lips over the 19/32" brass half-pipe. If I knew where it was at the moment, I would simply post pictures and/or a video.

 

I'd really love to see a picture or even a video. I'm wondering how the loading of the clip-fed RSCB worked. After you manually bulled the ram back and pushed it forward did you then need to aim the gun down to reload it? I would imagine the ram would do the job in a one-dart RSCB that had a clip feed but what about in your three-dart version? I assume you pulled back the ram three times in a row, then fired, then aimed down, fired, aimed down, repeat. Am I getting that right? Any chance there's already a thread or picture of it up on the net now? I'd happily search your posts on the forums if I thought it'd be worth it.

 

 

Putting the 1/2" straight through it as Ice said would improve the system. Set your 3d printed part up as a female connection for the PVC T so you can just plug it in. 

 

I'm now a fan of the McMaster PETG, I think it's this number 2044T43. FYI - shipping is like $20 for that long stick, so buy a bunch or buy shorter lengths if you use it)

PVC is super easy to chamfer, and will feed better than the 3d printed part. Just stick it through and chamfer it; only really worrying about chamfering the 3d printed magwell if it is between the dart and the PVC for some reason.

Look at Boltsniper's SCAR-N:

 

Yep, I think I'll be doing this. The only thing is that I'm considering printing the beginning of the 1/2" PVC that goes straight through the PVC tee as part of the magwell. The reason for this is that I'll be able to avoid having to bore out the inside of the tee joint since I can print this extension to exactly fit the two stages of width inside the tee joint. I will obviously also print a hole that allows the air to come up from the bottom threaded piece of the tee.

 

As for the barrel, I am considering 1/2" Sched-80 PVC. When it comes to compressed air guns, I find that a tight seal on the barrel like 1/2" CPVC will give you doesn't improve my ranges. I'll have a slightly tighter fit in the cone come right out of the magwell to ensure that nothing that gets pushed through can easily just fall out of the barrel if aimed downward. That's generally not even a problem with my Sched-80 actually. It has an 0.52 ID and when I seal one end a dart will not fall out even when shaken a little bit. Letting the seal (usually my thumb) up allows the dart to fall right out quickly though. I think that's probably a great seal for compressed air since air compression doesn't need to build up like in a spring gun.

 

You say that it will feed better than a printed part. Why do you think this? Smoothness of PVC vs printed ABS?

 

Boltsniper's SCAR-N looks awesome. I may, very well, try to copy this design on version two of this gun but for now I'm going to try to keep the complications down and go for ensuring it loads properly without jamming.

[Meaker VI]

As for the barrel, I am considering 1/2" Sched-80 PVC. When it comes to compressed air guns...

Right, air gun. I think the Mcmaster stuff I linked is airgun fit and .52" ID.

You say that it will feed better than a printed part. Why do you think this? Smoothness of PVC vs printed ABS?

Yes. You'd probably need to sand/smooth the printed part anyway unless you've got a high end printer. And PVC really is easy to chamfer - I usually use a regular pair of scissors. Beside that, you can seal with the manufactured PVC part easily, sealing with the printed ABS could be hit and miss, unless you design in an O-ring seal somewhere which just adds parts.

[jwasko]

The thing that a longer draw doesn't solve is 'bounce' in the breech caused by your pressure system charging the chamber suddenly- you'd loose efficiency. I think that Boltsniper talked about that while developing the SCAR-N as a result of observing it happen in the FAR. It also means you've got a longer blaster.

Here is what Boltsniper said (from the SCAR-N page on his website):
"The main unexpected issue with the FAR involved bolt bouncing.  When fired the plunger would travel forward and impact the rear of the bolt.  During this impact the entire bolt/plunger assembly would bounce backwards slightly.  This became an issue when the dart had not left the barrel when this happened.  When the bolt bounces back the pressure behind the dart is alleviated and there is no more propulsive force.  The dart exits the barrel with its own momentum at the penalty of barrel friction.  This impacts range.  Depending on the seal between the dart and barrel, the dart leaves the barrel and different times in the firing sequence and the impact on range is not consistent for each shot.  Some darts shoot 80’ and some shoot 50’."

If you look at the FAR, though, you can see why this happened so easily. The seal from plunger tube to shell/barrel was simply the front face of the plunger tube being held against the back of the shell (with an o-ring on the face). Any movement at all would break his seal.

The design I have laid out has a seal between a cylindrical ram and a tubular chamber, and would probably have at least 0.25 up to0.5inches of overlap, like your average slide breech.

In any case I would think that the air cylinder would hold fast against the pressure emitted from the firing valve. You may be totally right that bounce is an issue, but personally I'd be more worried about premature retraction in Dskippy's blaster. In a springer you're right, bounce would be an issue and some sort of lockup would be needed.

Actually, for both Dskippy's semi-auto air blaster or for a springer: perhaps a simple catch could be designed. When the trigger is depressed, it notches into the ram to keep it closed. When the trigger is released, the ram may retract (by air spring, etc).


Dskippy: Yes you have the concept exactly. It was sort of setup like a bolt action rifle. I'd turn the bolt/ram ~90degrees out of it's notch, and pull it back then push it forward to load a dart from the mag into the RSCB. I could do this 3 times if the RSCB was empty, and then I could point down-shoot up to 3 times. It was easy to add another one or two darts to the RSCB.

I liked the concept but never used it much because I had gotten used to having ~7darts at a time in an RSCB, and also because it was such a pain to get a new mag to lock into place (not a problem if you 3d print or even just adapt something from a Nerf gun).

Sorry to say I have no pictures of it on my Photobucket, so there aren't any on the web. I'll have a look around and see if I can find it, but I think it may still be at my parents' house so it's going to be a while unfortunately.

Edited by jwasko, 07 December 2015 - 09:15 PM.