23 replies to this topic

[wintermute]

So, I have decided to begin designing/building a homemade. Not sure when it will be complete but hopefully soon. My plan is going to be loosely based on carbon's SNAP 4, with the barrel parallel to and reversed - rather than inline - with the plunger tube.

I was going to try something I haven't seen before, and have two plunger tubes about half the length of carbon's desing. These we be joined with a pvc tee-joint before going to a single barrel.

My other idea was to have a shorter plunger tube with a greater diameter.
My reasoning is that both of these designs should be just as effective as the standard SNAP. They may be even better because the plunger(s) has to travel a shorter distance, and may deliver the air to the dart (stefan) more rapidly.

Just wondering if anyone knows of any serious issues with either these designs or if they have been done before and I missed it.

Feedback would be cool, and feel free to call me a moron if my idea sucks.

Also, thanks carbon for your sweet write-ups

[Prometheus]

Sounds ambitious. And difficult. Good Luck.

[Carbon]

I've played around with this idea, but never actually built a gun around it (I just hooked two SNAPs up to one barrel). The biggest challenge you'll have is creating a trigger system that can simultaneously release (and engage) two plungers...and making both plungers identical.

Thinking about it, you may be able to get away with two half-size plungers, without even increasing the tube size. Bigger plungers have greater mass, and will accelerate slower. If you use two standard-size plungers, you can make them lighter (shorter chargerods). Smaller plunger = lighter = faster travel. Larger tubing may negate the benefits...but honestly, I don't know. Definitely interested to see what you come up with.

[cappold]

I agree with Carbon. The major problem with two plungers leading to one barrel is timing. If the timing is not exactly perfect you will get turbalance (sp?) in the air behind the dart. I do not know the proper physics of it all, but what happens is the air from the barrel that arrives first will go to the dart and down the opposite plunger. This will work less than having it hooked up to only the first plunger. When the second plunger does hit, the dart will be gone and the extra power will be wasted. Even if the timing is off only a few fractions of a second, this will happen. Hopefully someone who is smarter than me can give you the proper lingo for what would be happening in this sceniaro.



This is sloppy at best but might help illustrate what I'm saying.

[wintermute]

hmm, I see what you are saying, and understand the physics (i think). pretty much: mis-timing may create turbulence-hence a low-pressure area- behind the dart, which may pull it back down the barrel.

I don't know if that will happen though. The volume of air between the dart and the plunger shafts will be shrinking rapidly, regardless of a slight mistiming, so pressure will build up. Also, I think I am more worried about a mis-time coming from inconsistencies in the seperate plungers rather than the trigger mechanism.

thanks for the feedback, and at this point I think that I am going to go for the double-plunger design after some careful planning, if worse comes to worse, I will still have two seperate snaps

edit: currently working on some rhino3d renders

Edited by wintermute, 30 May 2007 - 07:49 PM.

[privateer]

1) There is more dead space in a two plunger design
2) timing loss causes less energy transfered to the dart; the faster plunger shoots the dart from the barrel and the slower plunger does... not much.

Synching the two plungers would be a pain in the arse...


IDEA: one gun, two plunger chambers, TWO barrels. Along with a breech loading mechanism, that would make a bitchin primary. On a double barrel shotgun, there is one trigger in front of the other... you may want to try that set up.

Oh SNAP, I think I want one... yay new idea. Please excuse me while I steal my idea!!

(do what YOU wanna do, hope this helps)

[wintermute]

I'd like to know if anyone has actually tried to make a double-plunger to single barrel design.

Maybe a tight-fitting / telescoping barrel could allow the pressure to build and both plungers to fire evenly.

also, maybe it is a dumb idea, and I should try the "fat" snap-single barrel and plunger with a pressure chamber that is only 6-7 inches long but made from 4" pvc

still working on some renders, i'll get them up in a bit

[wintermute]

here are some renders of the double-plunger design...
looks awkward, but compact





I have also been toying around with privateer's idea, maybe something forearm mounted, like a super-manta

[Carbon]

Now that's interesting!

The trigger/identical plunger issue would still be an...issue, but this design would address the main problem of the SNAP-4....it was pretty uncomfortable to push the plunger forward the five inches it needed to go. Using two smaller plungers would allow you to use a shorter stroke. It you played your cards right, you could match up the length of the plunger stroke with the amount of pull needed for the breech.

Build it...I think it has real potential. If I can scare up enough parts, I might try it as well (if you don't mind).

[wintermute]

It you played your cards right, you could match up the length of the plunger stroke with the amount of pull needed for the breech.

Build it...I think it has real potential. If I can scare up enough parts, I might try it as well (if you don't mind).

Duh!!!

wow carbon, I didn't even think of attaching the breech to the plunger handle. Man I am dumb. I'll get started with basic construction soon as I get some time/fund$


And I wouldn't mind at all if you built one of your own. You can probably execute the idea a hell of a lot better than I can.

as for that breech, I haven't made one before, but what is the standard pull length needed for a stefan?

[Carbon]

as for that breech, I haven't made one before, but what is the standard pull length needed for a stefan?

Depends on the size of your darts. My stefans are 2", and the throw of my breech is 3.25".

The more I think about it, the more powerful this idea becomes...

A typical SNAP plunger has a stroke of about 5". The throw on the breech is 3.25", like I said. So, that becomes the plunger stroke. So, we're getting an effective plunger stroke of 6.5"...so, a 30% increase in air volume, with potentially a faster delivery (because of two lighter, shorter plungers)...

Wow.

[wintermute]

alright, I'm going to rework those renders to rough dimensions enabling the plunger and breech to be connected

question: will a breech still allow for a telescoping barrel and a tight fit? It seems to me that a breech may not load correctly if the barrel is tight on the dart

[Prometheus]

Depends on the fit of the dart. It might fit well in a progressive barrel, as long as it isn't too tight of a fight in the first stage. I would recommend 17/32", then 9/16", the 19/32", if you want a progressive barrel.

[Carbon]

question: will a breech still allow for a telescoping barrel and a tight fit? It seems to me that a breech may not load correctly if the barrel is tight on the dart

By telescoping, do you mean nested?

My stefans are pretty tight in 17/32", enough that a straight breech load doesn't work. The back end of my breeches are made of 19/32", about 1" or so. When the breech closes, it shoves some of the dart into 17/32", enough that it fires well. So, you could start with 19/32", then have the starting bit of 17/32", then step your way up the sizes.

[wintermute]

(for reference, the barrel-including breech-is 12")

here is v2.0
Looks like I need to redesign the pimo handle to make it lighter. Something like the slider on the SNAP-4 would be ideal, but I don't know if my pvc skillz are up to that level. The slider would make also open and close the breech. The current design would require awkward barrel twisting.

[Ronster]

You know, this design would allow for actual bullpup.
If you moved the handle a bit more forward, the clip could slide down between the two pluger chambers and you won't have a tower of darts obstructing your sights (that's if you're going to use a clip like the SNAP-4).

[CaptainSlug]

You don't really need to have the plunger rod exposed. You will be using hex bushing adapters for the front end of the plunger chambers so you could hide them with lengths of pipe with a slot cut in the side facing the center.
Then connect the two plunger rods with a pair of threaded rods.

The handle that extends from the breech could simply be behind the threaded rods that link the plunger rods so that it pushes them forward but still allows you to pull it back before firing. You could even spring-load the breech if you wanted to then use a gravity clip.

[Carbon]

This is getting interesting.

I spent some time tonight digging around in parts, seeing how this thing would fit together. I ran into a snag with the air delivery end of the plungers: elbows and tees take up too much physical space for the plungers to sit close together....not pleasing. So I got to wondering...why not run the barrel between them?

This is a mockup:



It works out rather well: the breech will be in a direct line with chargerods, so everthing can get a more-or-less straight pull. Plus, it means wit will be fairly staightforward to link everything together.

This will get built this weekend. Time to start hacking on that trigger....

[wintermute]

wow carbon, that looks quite sexxy

you could use what captain slug said and just use the barrel to prime the gun, possibly aided by a handle

I'm anxious to see how it yours turns (it feels good to inspire a god of homemades)

I think I'll be getting some parts this weekend, and begin some construction.

[zaphodB]

If the handle that primes the plungers is able to slide on the plunger rods, you can keep it attached to the barrel, which will allow for easier priming. With the weight of the priming handle eliminated from what the springs have to move, the gun will also be able to move the air a little bit faster

Putfile

sequence is fired, loading, primed

The placement of the breech on the pictures is arbitrary.

Edited by zaphodB, 01 June 2007 - 01:41 PM.

[wintermute]

here is a cycle of carbon's version (any probably most versions considereing the pipe fitting sizes)



add a clip = pump action

a handle on the bottom could add more leverage for priming

[Liam]

That would be very hard to build. But I hope you get it to work

[wintermute]

So here's the deal:

I have acquired a few PVC parts, but time and money for more parts is looking slim as of right now. I want to keep this idea alive, and hopefully I can gather parts and what not to finish this by august.

Two questions:
1) carbon, any progress on yours?
and 2) where can I find the rubber fender washer for the plunger?

[Carbon]

Two questions:
1) carbon, any progress on yours?
and 2) where can I find the rubber fender washer for the plunger?

I had a car die on me over the weekend, so that's killed a lot of free time and money. I'm hoping to get a little done over the next few nights. Rubber fender washers are easier: check the small fasters aisle at Ace or True Value...they keep them in the Wall of Tiny Drawers®.