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Venaticora: katana mag, pump action, monocoque receiver


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#1 Sin Phi

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Posted 29 December 2017 - 06:45 PM

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https://imgur.com/a/5FDmp

 

A design I have been refining over the past month. I did one a few years ago when I saw the FAR, but the Caliburn and the rapid improvements in 3d printing inspired me to give it another shot. Obvious comparisons will be made to the Caliburn because that seems to be the standard and although this started differently I converged on some of the same design decisions (trigger group was a place where I iterated a few times and came back to the dual lever).

 

The drivers for this design that would set it apart from other homemades is the ease of servicing, low deadspace and durability. For servicing there are 7 M6 bolts or push pins to field strip. The durbabilty is there with no threading of 3d printed parts, metal strips or the receiver and the monocoque receiver. Receiver is a 1-3/4"x1-1/2" polycarbonate tube, like the transparency and material properties. Will fit a [k25]/[k26]/K13 spring. 1.5" of pre-compression and 6.25" of compression with a 1.5" OD plunger chamber. I copied the spring compression scheme of the Caliburn as I haven't experimented with [k26] springers before, just going to assume it has got it right. O-ring seals for plunger, double on bolt, and trunnion has one to cushion the front of the bolt.

 

There is only 2" of dead space and a 0.5" bore in the bolt. The bolt seals with a 9/16" brass over the 17/32" breech. It is a sort of reverse sleeper breech, can not have the dart finger on the bolt, so it is instead on the breech. The idea is the dart will slide into the 9/16" as it pushes forward, halving the deadspace over a pusher design. The bolt could be used as a pusher simply by putting brass that will sleeve inside 17/32" in the rear section.

 

The barrel and breech are separate pieces, allowing for easy barrel swaps depending on the darts, spring or desired muzzle device. The breech is secured with a bolt/pin to lock in the correct head spacing. The barrel could be 9/16", 17/32" or any combination of the two. The only requirement is that there is a ~1/2" collar of 9/16" to seal around the front of the 17/32" breech. outer barrel should be <0.75". In my renders it is shown with 18mm carbon fiber tubing to support the brass.

 

The priming arms to connect the bolt and foregrip are exactly 12". This simplifies part sourcing. You could even use carbon fiber strips meant to reinforce musical instruments. The receiver will require mostly simple machining, the only difficult part is the long slot. Doable with a drill and coping saw.

 

Magazine is a bit of a difficulty. It is sized for a katana mag, I used the bumper STL to make sure I had the profile correct. However the catch is much lower, really the catch on the katana mags is very high compared to nerf mags. I could make it work with the katana catch location by reducing the length of pull, going for a button catch with cross bar (most likely one I would try), or putting the mag release on the front of the mag well, but didn't want to make that compromise. Not sure If it is acceptable to expect a modification on the magazine to use and also don't have a katana mag on hand for exact measurements (would need position and dimensions of catch retaliative to the bore axis). I have designed a 12 dart version of the mag, feed lip profile is different (scale-able).

 

For ergonamics, 11.25" length of pull (but plate to trigger, about 1" longer than Caliburn). ~28" overall length with a 12" barrel. Furthest part of foregrip is 25.75" from the buttplate and 4" long. Pistol grip is modeled after a magpul moe for ar, cross check dimensions with my paintball marker (Tippmann A5).

 

Magenta parts are to be 3d printed. The clear components are polycarbonate (other than magazine). The controls could be either.

 

Another idea I had was to use a brass liner for the plunger tube (resizing plunger and bolt appropriately) to reduce seal drag. Didn't see any examples of this being tried, might be very similar to aluminium tube performance.


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#2 Meaker VI

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Posted 29 December 2017 - 11:47 PM

I'll say what I said about this before:

 

Slooottttsss....

 

But really, machining for that will be a bear compared to the Caliburn. Although removing them might make the blaster weaker, doing it would also make it easier to reproduce.

 

So I'd ask what your goals are. If your goal is to have an optimum-performance blaster, this may meet that criteria. It is not easier to build (or produce) than the Caliburn, if your goal is mass production or even mass-replication (end user builds their own). And I say this may meet the criteria because at this point, no one knows how this will perform as it doesn't appear you've built one yet. Reducing the breech volume is a good goal if it works as intended. However, it might be a better use of your resources to design the breech to work in the existing Caliburn platform ATM, as that is a known variable that has such a wide impact (200+ blasters built by Slug with numerous parts kits and probably a few self-builds out there).

 

I further get what you're attempting with the short-dart-only mag well, but consider that it is ultimately saving ~1.5"-2" of length in exchange for requiring 3rd-party mags that aren't in ready supply at the moment. Using a full-length magwell would mean compatibility with the Katana system, and all the regular mags and half mags already out there. Yes, it'd mean slightly larger parts and the breech might have more deadspace when firing half-lengths but, until you've convinced me that this would be easy to build, reducing part volume doesn't need to be a goal.

 

Interesting idea about brassing the PT. Personally, I feel that's probably overkill and not substantially better than aluminum (or even just PVC) with the parts we're using. A highly-machined precision build might benefit, but it's probably still a marginal gain at best.

 

Also, it is possible to host images natively to NH, and has been for awhile now. Here, for posterity because your drawings are pretty:

 

Breech volume comparison, Longshot, Caliburn, Venaticora:

K3ulpMw.jpg

 

Assembled View:

rl0hzAG.jpg

 

Exploded View:

IhnmDYm.jpg


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#3 blitz

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Posted 30 December 2017 - 11:18 AM

So, just a few thoughts from me. Let me say that I fucking love this design and I don't want to be harsh.


1. Meaker's point about Katana propriety is super valid. I love the idea of both katanas and this build using them exclusively, but they just aren't super avaliable and people don't have them. While I am likely going to convert over at some point, I also really love my artifact mags. (Maybe design an alternate for standard mags???)

2. The pump grip section should not be 3d printed, please lord. A big problem with the ESLT was the 3d printed pump grip cracking due to the strain. The pump grip tube should be a casted pipe (e.g. pvc or something similar) because it's much stronger. The picatinny on the bottom can be printed, no problem. 

 

3. Just because I don't trust 3d printed parts, I would really beef up the catch pieces and maybe even make it a single part with the stock/spring rest. Seems like a way to increase the longevity of the design and also make it more idiot-proof (attaching one piece to the tube instead of 2).

4. What is the tube that you plan to be using? I realize that the OD is 1.5", but what about ID? Is this compatible with 1.25" PVC?

5. I really like the increased airflow of the brass (even though I hate brass. Seems like a lot of potential for designing alternate breeches (e.g. artifactoid)

6. I may have missed something, but it it possible to remove the piston/barrel/breech assembly by removing the bolts at the front and at the breech? If so, that makes maintenance really really easy and I love that.


I can't wait to see a finished model!

 


Edited by blitz, 30 December 2017 - 12:50 PM.

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#4 Snoop Doggy doge

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Posted 04 January 2018 - 06:05 PM

I love this and I hope to see it developed further. IMO slots aren't that much of a bitch and add strength, which I would prefer if this was my blaster, but I see the slot less points to make it mass production. 

I don't have too much feed back besides stuff already mentioned, however I think the pic rail section on the back needs some sort of help to mount as it might be a bit wobbly, and the stock might need to be reinforced / enlarged because it looks a little small. 

Otherwise, I'm very excited to see where this goes! I like this a lot!


Edited by Snoop Doggy doge, 04 January 2018 - 06:08 PM.

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#5 Birch

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Posted 04 January 2018 - 07:34 PM

I think that from what I have heard and seen regarding the Caliburn design, this offers a major improvement, provided you have access to katana mags. 

 

The main three complaints I have heard about the Caliburn:

1. The build feels insecure and kind of "twisty"

2. Because of the use of bolts for the frame, it can be very knit-picky to assemble correctly, as you have to tension each of the bolts and nuts correctly

3. There are a few parts (although I think many have been re-iterated and fixed) that are relatively weak, or not designed the best, like the piece above the mag-well

 

However, it seems to me that this design addresses each of those complaints wonderfully, and personally from what I have seen thus far, I would rather build this than a Caliburn. Also, if the creator is planning on distributing this design a la Slug, than as long as he has a mill those slots will be hardly a nuisance. Even for people who don't have a mill, I think that a dremel, a drill (press hopefully), and some patience are just fine for making slots. Honestly I would rather machine slots than have to tension a bunch of finicky bolts myself. I really, really like the bolt design, and just the whole design in general; great work and will definitely make one if I can get access to a 3d printer or can buy the 3d-printed parts, as well as if I can buy some katana mags.  

 

However I do have a few suggestions:

1. Shorten the draw: 7 inches of draw on a 1.375" id plunger tube is honestly kind-of overkill. Either put a 18"+ chicago barrel on this to actually take advantage of all this volume, or shorten the draw to 4.5-5.5". I have run into a ton of longshots with [[k26]] or k45 equivalent springs that get better performance than some +bows, so I really don't think the extra volume is worth the extra length and priming effort. 

2. Change the pump design: just like Blitz said, 3d printed grips are prone to breakage, and personally I would much prefer a 1.5" pvc tee over pretty much any design people have tried printing (1.5" pvc tee's are wicked ergonomic)

3. As far as I can tell, only the grip pieces are actually 3d-printed, but personally I would try to 3d print the whole receiver assemply except for the the sear, which should definitely be a machined part.

 

And just a p.s., if you somehow have access to a lathe, I think lathed bolts are really beneficial for blasters like these, and would be a great improvement!


Edited by Birch, 04 January 2018 - 07:42 PM.

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#6 Meaker VI

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Posted 04 January 2018 - 10:32 PM

Honestly I would rather machine slots than have to tension a bunch of finicky bolts myself. ... as well as if I can buy some katana mags.


Having built a Caliburn and slot-based blasters, the difficulty of tensioning the bolts is way overblown. It took me a couple of hours to build the Caliburn while not paying full attention to it and going to do other things. It took a few minutes to get the rods all lined up and behaving, another few to crank them down.

Slot cutting without a mill or router table/jig (i.e.: with more tools than the Caliburn takes to build, but still a basic modders kit) takes longer than the tricky parts of aligning the rods. But it does produce a more monolithic part that should be sturdier.

Re: Katana mags: your reply is an example of the reason Id prefer to see this full-length compatible. Very few nerfers have Katana mags presently, and Katana mags are designed to be backwards-compatible with regular mags. So a full well will work with everyones kit AND Katana mags, but a short well only Katana mags.
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#7 Birch

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Posted 05 January 2018 - 09:45 AM

While I think your point about katana mags is totally valid, honestly I would probably only use a blaster like this with them. The reduction in deadspace is a huge advantage in my opinion, and buying katana mags isn't that much of an issue to be honest. 

 

Also, while you may have had a good time assembling the caliburn, you can't deny that the rod system is a little janky and kinda hard for amateurs to assemble, while a receiver with slots pre-milled would essentially be idiot-proof.  


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#8 Meaker VI

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Posted 05 January 2018 - 05:49 PM

Also, while you may have had a good time assembling the caliburn, you can't deny that the rod system is a little janky and kinda hard for amateurs to assemble, while a receiver with slots pre-milled would essentially be idiot-proof.  

 

If it was premilled, yeah that'd be easier, though know that I've seen posts from plenty of amateurs having just as easy a time building it as I did. But you're adding a ton of work for the guy selling the things doing it that way (vs. cutting parts to length). IF another way exists or could be pursued, I'd encourage OP to try to follow it. I'll grant that I'm not sure what that is - I was struggling for months trying to build a printed version of the Caliburn without slots or rods.


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#9 Snoop Doggy doge

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Posted 16 January 2018 - 01:40 AM

#FIRSTrobotics kids remember all the nuts that litter the damn field after the game
I honestly hate using any lock nut after that because even with Loctite blue it's ehh. 

I wonder where this Sin Phi guy is and why he didn't respond, because he was active on Jan 7.
I think an advantage to possibly this long of a draw is maybe an even lighter spring with a short barrel. I forgot, this is going to be a lot of volume and no barrel to seriously take advantage of it is a bit of a waste. 

TECHNICALLY anyone can cut slots, you need a drill, hacksaw, sandpaper and patience to make them nice. 
Or a sharpie + tape + dremel. IMO they aren't that bad and are great structurally. I prefer them,

Katana mags are ok and I see them being really useful so I wouldn't mind running them with this, as why are you running full lengths with a blaster like this anyway but I get full compatibility. 

//please make this public I love this thing so much


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#10 CaptainSlug

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Posted 16 January 2018 - 08:36 AM

If the trunion piece that the barrel attaches to had a more robust connection to the plunger tube AND secures itself to the barrel more rigidly the barrel itself could be used as the slide for the front grip.

 

This is of course assuming that the barrel material is thick enough and strong enough to support that offset load. But it could be supplemented with another nested tube over it. The design could be revised slightly to completely negate the need for slots.

 

Lastly, I think it's a terrible terrible idea to transfer the shock from the plunger slamming into the bolt through the bolt itself. Your ramrod is not going to be strong enough to handle that impact and it will break. The ramrod itself is only strong enough to handle loading darts, and unless you make it out of aluminum the force of the plunger slamming into it will destroy it. You also WILL NOT be able to reliably feed darts through the middle of that o-ring anyways as it will add considerable friction to the process and could peel the foam back from the heads of the darts.


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#11 Sin Phi

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Posted 24 January 2018 - 03:03 PM

I have put this on hold because I will not be able to do a build until summer and the feedback seemed to be counter what my initial design goals were. I am going to continue to iterate until I get to the point for a build, so going to try to respond to all of this great feedback now. Made all  my responses in order of post.

 

The goal is not an easier to build blaster. It is for something that is more durable and with ease of serviceability. I am not that concerned with the difficulty of slots, they are good for the attributes I want. These are also easy to create a jig for, which I will be doing. no considerations for mass production, this will be a DIY project and CC BY-NC-SA 4.0.

 

It is not designed for PVC, it is polycarbonate 1.75-1.5" tubing. Better stiffness and way higher impact resistance. Would not be compatible with any PVC sizes for the upper receiver.

 

For the half dart vs. full dart argument, if I had to design for full darts I would just say go with an existing design. If there is no value in a half length only blaster I don’t see much point in going forward with this. Using the half length gives me several design wins. Shortens the maximum arm extension; better ergonomics and arm angle for priming. The bars on the charging pump can be exactly 12 in, good for part sourcing. Cuts a big chunk out of deadspace. Reduces the mass, overall length and print volume.

 

I will say I may have been mistaken at the prevalence of katana mags by seeing the nerf community mainly through the sort of people who are always onto the latest thing.

 

Are pump grip 3d print failures on the caliburn an issue? Would be easy to design something to use a tube for the outer part of the grip, but without serious milling the inner portion will still be 3d printed.

 

Breach designs are very interchangeable. Pusher or sleeper style brass could be done with the same bolt. Others might require a different trunnion.

 

Some notes on disassembly. The butt-plate should always be removed first during servicing so that the spring is not under tension. The only operation you can do without this is a barrel swap. That could be done without removing the front cap, but it may make it easier if it is removed. The barrels are friction fitted into the trunnion. To remove the plunger, only the butt-plate needs to be removed. To get the bolt out is more involved. First the butt-plate, then lower receiver, next the trunnion and front cap.

 

The rail section will be permanently glued to the upper receiver as seen in the exploded view. Should be no issues with durability.

 

The draw and preload are exactly the same as the caliburn, if those are not desirable I can adjust. Would not be able to have variable draw lengths once built due to seer design. Already planning on testing some really long barrels.

 

The lower receiver might be able to be 3d printed, but it has one very important high impact job, the two upward facing teeth are what catch the bolt when the plunger impacts it. Not sure if PLA is up to the task there.

 

As to lathed bolts, I have drawings done for HK style push pins. Could mill or 3d print the bodies and make springs from wire.

 

I explored using the barrel as the charging arm, but then you need a push forward stoke to load instead of just pumping. Also makes barrel swaps a bit of a pain. There are some interesting designs I can think of using that method, just not for this blaster.

 

The bolt does not transfer the plunger shock to the ramrod, it goes into the lower receiver. Again see the teeth on the top of the lower receiver in the exploded view.

 

The o-ring in the trunnion is easy to leave out if it causes feed issues, it is not necessary to the sealing with a brass breach.

 

*had tube ID wrong


Edited by Sin Phi, 24 January 2018 - 05:51 PM.

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#12 CaptainSlug

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Posted 24 January 2018 - 04:55 PM

Are pump grip 3d print failures on the caliburn an issue?

They haven't broken under normal use. They do however break if some of the screws escape and the end user doesn't notice and continues using the blaster. The rear screw holes in the printed part will rip out eventually if those are the only screws installed.


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#13 Meaker VI

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Posted 24 January 2018 - 05:27 PM

RE: Mass production - then ignore most of my complaints; you can make something as difficult/easy as necessary if it isn't for any kind of production.
 

It is not designed for PVC, it is polycarbonate 1.75-1.25" tubing. Better stiffness and way higher impact resistance. Would not be compatible with any PVC sizes for the upper receiver.

 

That's actually pretty close to 1-1/4" sch. 40 PVC (1.66" OD & ~1.35" ID). Probably could get it to work just by swapping orings.
 

For the half dart vs. full dart argument, if I had to design for full darts I would just say go with an existing design. If there is no value in a half length only blaster I don’t see much point in going forward with this. Using the half length gives me several design wins. Shortens the maximum arm extension; better ergonomics and arm angle for priming. The bars on the charging pump can be exactly 12 in, good for part sourcing. Cuts a big chunk out of deadspace. Reduces the mass, overall length and print volume.

There is value, if you are fine supporting the blaster's unique demand for a unique mag. Once half-length mags are standardized and wide-spread, it'd be less of an enigma, ATM it's just the katana and custom systems. There are also several full-size mags that accept half-length darts, using one of those would mean all your internals stay at 1.5" stroke length, but your magwell is ~3" long.

 

will say I may have been mistaken at the prevalence of katana mags by seeing the nerf community mainly through the sort of people who are always onto the latest thing.

It's just the only marketed half-length mag ATM. Hopefully someday there will be wide availability and a standard, but for maximum compatibility a full-length magwell is needed. As I said above, if you're fine with it and you're only interested in building the one, it's up to you.


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