Shotgun Idea

[renegadecow]

So this design has been floating around in my head for some time now. It should work, or at least my limited understanding of physics says this is gonna be *fruitcage* awesome. And since it's so simple, it could in essence be used in making anything from a good old double barrel shotgun to something automated like say an AA-12. Here's how it goes:

You load the barrel by putting the TM shell against the breech, which also acts as an air seal of sorts. BBs empty into the barrel up to the hop up. When fired, gas is shot through the inlet on the side and out goes up to 30bbs, potentially speaking. All shelled systems have the gas go through the shell itself; that's not due to how gas flows, but because it's the only way to get the bbs out of the shell. Since TM shells are spring loaded, bbs are dumped into the chamber. The gas reserve would of course have to be stored in the gun itself as whatever magazine system employed will be holding the shells.

[heikis]

first, try blowing a single bb through the barrel. you made it? cool!

now try blowing 30 bbs stacked together through the barrel. let me know how it goes.

[renegadecow]

To get it within usable speed (about 220fps), you'd need 14J to push out all 30 .20g bbs. CO2 can do that easy, or were you suggesting I put my mouth at the inlet port?

[TnL]

i would put a real breech seal, I dont quite think the TM shotshells are airtight...

otherwise, sounds like an awesome idea, double barrel, gas in stock, 30 BBs at a time would be worth only 2 shots,

[bobthebuilder]

The theory is solid enough.

But your problem is getting enough gas, at enough pressure, to push 30 BBs to a useful velocity. Most other models only go as high as five BBs per shell. 30 makes life very difficult. To get enough power you'd be dumping quite a lot of gas per shot.

 

If you where going to play around with it, I'd say that starting with an external HPA rig would be your best bet. I suspect anything else will have to many issues with both cool down and reservoir size.

[Tommygunn]

Would there not be a potential safety issue? If only one bb was released, due to a faulty shell, you'll then be putting 30bb's worth of gas behind that one bb. Could sting.

 

Tom.

[bankz5152]

Sounds good. Really need 30 round spread! Id be happy with 10 or 15

[renegadecow]

Now, that's why I put 30 rounds "potentially". For something more usable and economical on gas, I'm thinking more like 10-15. My main point is being able to use TM shells whose copies are just about the cheapest shells you could get. Regarding the air seal, the shell alone isn't air tight, but being crammed into a chamber with the back shut either by a bolt or breech face can get you the needed pressure spike.

 

Fair point on the safety issue Tommy, it's one shared with Marushin M500s. It's possible to get a TM shell to jam up (on specific brands of bbs), but from my experience only with intermittent feeding like on conventional shotguns they're made for. But if you leave the catch open to dump all its contents, the inertia of the bbs as a whole pretty much clears it out all the time.

[hotelkilo]

and what if i only loaded 1 bb into the shell before firing, massive 'over-power' potential imo.

 

current airsoft guns traditionally run about 1-1.5j and u want to go to 10x that? 

[TnL]

and what if i only loaded 1 bb into the shell before firing, massive 'over-power' potential imo.

 

 

then you'de be banned for willfully exceeding the fps limits, and also probably charged because of caused bodily harm, so thats your problem and your responsibility if you do that

[Shardik]

Similar to purposfully running a HOT AEG.

[shmook]

I am in no way an airsoft tech, but I see some immediate problems.

 

First, air seal at the breech. You mentioned a sealed breech, but that may only work for single shot, a la double barrel. As soon as you try any semi auto mech, the pressure involved would overcome seals.

 

2nd, pressure involved. It would need to stupid high, as you stated. Not only is this bad if 1 bb gets launched, but you would need a huge tank for it to be useable in game between refills

 

3rd, would a TM shell unloading over the distance between breech and hop have enough force to overcome the hop rubber, spilling bbs for each cycle? No idea really, just a thought...

 

I love it though, and if anyone cam do it, you can! Please do and make eleventy20 of them!

[Inari]

Good thinking.

 

The idea of "what if I used this to hurt someone" is a bit of a silly argument, because the same can be applied to all current guns in use. There is a lot to be said for being responsible - if you do not believe people can be responsible, then you have a problem because that very argument is used to attempt to ban airsoft in a great many places.

 

To overcome the hop issue, use an R-hop style contact patch with a larger surface area.

 

BB wise I think between 5 & 10 is plenty, which means the power doesn't have to be as great, and also allows you to ramp up the spring tension in the shell, mitigating the risk of a misfeed. 

[sandstorm]

The problem with 'just load 1' is the same as Dan Wesson revovlers. How do you check all the shells peopel carry on field during game, when it matters? Well, you don't, so this / these would get banned on general purpose of avoiding the pain. Which is why it should be addressed as soon as it can be.

 

Otherwise, really neat idea. Harder to sell to anyone to make than the China Lake, though, what with there being no profit in selling extra shells.

[heroshark]

how about a rotating shut off to the feed, similar to an m500 chamber but much smaller.

[renegadecow]

^

Because that would be no different from my Serbu and the TM adaptable M500 you made.

 

@Shmook

Looking more into the shells, it seems the air comes out between the hull and the brass. Just the walls of a chamber should be enough to address it and the bolt would just be there to keep the shell from flying out.

 

and what if i only loaded 1 bb into the shell before firing, massive 'over-power' potential imo.

What if I load hard rubber shells in a grenade launcher?

What if I swap the cylinder mid game in a WE Katana M4?

What if I don't call my hits?

What if I bash the butt end of my rifle into someones face?

The answers to which is, will you really want to be doing those to your friends?

 

And as said, you'd be needing 14J to pump out all 30 bbs at a respectable velocity. That's theoretically speaking, but not exactly my intention. On a green gas NBB system you can get 4J, a whole lot safer than 14J and enough to propel up to 10-ish bbs to some distance. 

[PureSilver]

I think this is an idea with awesome potential. The first issue I see is the one TnL raises:
 

i would put a real breech seal, I dont quite think the TM shotshells are airtight...

 
The BBs in the feed tube may create enough resistance as they move through the hop-up and barrel to sustain quite some pressure behind them, and that will surely blow a TM shotshell inside-out. Like you say, though:
 

Regarding the air seal, the shell alone isn't air tight, but being crammed into a chamber with the back shut either by a bolt or breech face can get you the needed pressure spike.

 
Putting a proper valve (e.g. a ball valve) ahead of the shotshell's feed would seal the rear of the chamber totally, removing the need to seal against the shotshell and protecting the shotshell against the pressure of firing. You could also 'meter' the feed in this manner - e.g., by making the feed tube only x-number of rounds long, so that when the ball valve is opened the shotshell feeds until the feed tube is full, at which point it can't physically feed any more, and when the ball valve is closed you fire only x shots. If a TM shotshell can hold 30rds three volleys of ten or two of fifteen should prove more than adequate. Limiting the gun to 10-15 rounds (as opposed to 30) also means a smaller energy input, reducing the potential disparity between correctly (fully loaded) and dangerously underloaded muzzle energies.

 

I like ball valves for their simplicity, affordability, and excellent seal - if a ball valve can hold back a hydroelectric dam, it can hold back an airsoft gun - and because I think it would suit break-open shotguns well; they have a rotating action involved (closing the breech), and a simple arrangement of gears could open a ball valve as the gun was broken open, and close it as it was closed.

[renegadecow]

Only one way to find out then: cobble up some PVC pipes together and make me a zip gun.

[hotelkilo]

 

What if I load hard rubber shells in a grenade launcher?

What if I swap the cylinder mid game in a WE Katana M4?

What if I don't call my hits?

What if I bash the butt end of my rifle into someones face?

The answers to which is, will you really want to be doing those to your friends?

 

And as said, you'd be needing 14J to pump out all 30 bbs at a respectable velocity. That's theoretically speaking, but not exactly my intention. On a green gas NBB system you can get 4J, a whole lot safer than 14J and enough to propel up to 10-ish bbs to some distance. 

 

if u load solid rubber 40mm training ammo into a gas powered launcher thats no longer airsoft

if u swap the cylinder mid game thats cheating

see above

thats either a deliberate act ie an assault or an unintentional injury ie an accident

 

no i wouldnt do any of those things intentionally either to my friends or anyone else i might come across, however i dont play airsoft against my friends. i play against large numbers of ppl i have never met before and may never meet agin and i have no idea of their background, intentions, agenda or general levels of sportsmanship.

 

and im not suggesting only loading 1bb deliberately to cause injury, what if i did it by accident beacuse i got my shells mixed up or thought it was fully loaded shell when actually theres only 1 or 2 bbs in there - ever done that with the mags for your aeg mid game cos i sure have, 

 

what you originally proposed would make a nice project for a 1 off creation for a talented and responsible player/collector but the idea of releasing 14j of energy per trigger pull seems a bit much for the average walk on type imo. 

 

4j, whilst still high, seems much more reasonable (and achievable)

[heroshark]

^

Because that would be no different from my Serbu and the TM adaptable M500 you made.

No just as a gate to shut off the feed entry to make the air seal. So it opens lets the rnds throug then closes

[renegadecow]

Ah, well, kind of like the ball valve PureSilver was going on about. We'll see. The concepts themselves aren't too difficult to rapidly prototype, it's the getting-them-all-in-a-working-gun where things get hairy.

[notrabies]

Well I'm not sure how much it'll apply here, but I think there are work arounds to the velocity problem.
While I'm no expert in how its done, the Maruzen M1100's can fire 1 bb at about 330 fps, and then without changing anything fire 10 bb's at some where in the low-mid 200's. If you can find one for cheap to experiment on, it might be worth looking into.

Gas shotgun dynamics depend on everything from temperature, to the type of load fired, to barrel and hopup friction, airseal, and a zillion other factors, but I'd severely doubt you'd need anywhere near 14J of energy to shoot all 30 bb's, considering I can shoot 10 at comfortable velocity at 1J.

[ED-SKaR]

Energy creep:

 

10 BBs weigh ten times as much as one BB, that means that they accelerate much slower, gives lower FPS right? Wel yes, but no. Because the pressure will build up more behind slower BBs and you end up with more power when using more BBs in other wise identical setups.

 

You really have to trial and error to see what kind of FPS you achieve with different weights and amounts of ammo.

 

 

 

I would still recomend setting up the gun for about 350fps with a single .2g bb, because that way if it does underload, you wont get a through and through injury...

[renegadecow]

There's that too. Honestly I just used an fps calculator to get that 14J number and I'm not sure how extensive those calculations are. I suppose an easy safety measure would be to keep  the inner barrel short so that the fewer the bbs, the slower they'll shoot out. Assuming a whole bunch of bbs behaves like one very heavy bb while in the barrel, only higher energy transfers would happen in that situation.

[CatgutViolin]

Looking at just the energy involved is not accurate because this is dealing with some fairly complex gas dynamics. A Maruzen M1100 can spit one BB at 1J with the same amount of gas required as firing ten BBs at 0.5J each- that's five times the energy for the same amount of gas.

 

I think firing 30 BBs at once with a usable FPS is very doable, and an external air rig could probably provide the requisite power at no more than 200 PSI. Have you given thought to what kind of weapon you'd be designing? Considering it'd function like a grenade launcher, with each shell providing one shot, it seems to me that something like a double barreled shotgun would be a good application.