SpudFiles

Right, I've had it up to here with auto-pistons, time to try something different.

I've been wanting to try hammer valves for a while now but never built anything, seeing the remarkable working designs ant has posted recently was an inspiration to try something along those lines, that I might finally see a working air-machinegun.

Following the ideas developed in this thread, I've come up with the following practical design. How it works should be pretty self-explanatory, the bolt is pulled back and caught by the trigger. This allows the sleeve to move back and seal off the barrel. Pulling the trigger allows the bolt to accelerate forwards, which strikes the valve stem, opening the valve allowing the compressed air to push the bolt back and eventually escape through the barrel and fire the round. If the trigger is still pressed, this should in theory allow a new round to be fed and the cycle to be repeated.

Looks complex, I know but the idea is to build it in stages - bolt and valve unit first to see if it will cycle, then add the barrel to see what sort of power is available, and if it's worth it get on with the trigger mechanism etc. I reckon I could built the guts in a couple of weeks, thoughts/suggestions?

Looking good, only question is what are you doing about a mag or hopper?

MrCrowley wrote:what are you doing about a mag or hopper?

Not a big concern at the moment, depends on what this will be for. Assuming it works, if I use it docked to my compressor then I'd want a hopper type mag for extended bursts, but if I go for something more portable, probably a spring loaded overhead mag, "It's me bren gun!" style

Haha okay sounds good. So possibly bigger cannons from now on?

This is still intended for 6mm calibre - smaller bore means you get more shots for a given air supply - it might be scaled up for marbles if it works some time in the distant future. I'm not sure about the reloading mechanism though. If I get the bolt and hammer to work succesfully, I can either build it as is, or have the air feed into a development of my cartridge design - I still want to see that brass fly!

Bigger then a syringe is all good with me

Oh I know the feeling, maybe you could make one just for looks, like a blowback bolt, except instead of returning the bolt, it launches empty brass out the side.

Sad maybe, but it'd have a similar effect.

The way I visualise construction the bolt will travel in a syringe tube

I could reverse the direction of the bolt travel, as in the original idea, and have the bolt extract the cartridge on the firing stroke - but that would involve adding some sort of rim or groove to the cartridge body, something I'm trying to avoid if it's to be mass produced.

You can get the PVC so why don't you go slightly larger?

What scares me is bigger project = more materials used = more materials wasted if everything goes tits up - remember, double the calibre means 4 times epoxy usage. The biggest issue really though is air economy. Let me see if I can get this to work for airsoft/pellets, then I might be inclined to go larger. Just think of the sort of bolt spring you'd need to cock to open a 3/4" valve, even at say 100 psi

I mean keep same caliber, just go bigger chamber if performance says so, if performance says nay and a syringe is enough, so be it.

The syringe tube in the design is the smaller tube that the purple bolt is riding in, the chamber is the bit to the left, that can be as big as I want it to or (for the experimenting stage at least) just hooked up directly to the compressor.

Ah right of course, forgot about that...

The way I visualise construction the bolt will travel in a syringe tube

<A HREF="">Damnit</a>

I like the design of the main unit, it took a minute (or ten) to fully understand it but i think i get it well enough. How were you planning on attaching the barrel? I thought that it might be difficult without "inserting" the barrel into the bolt housing.
The more i look at it the more i like it- it doesn't look toooo difficult to make, and with a nice compressor a marble sized one would be fun.

Novacastrian wrote:How were you planning on attaching the barrel?

Wild guess, taking a stab at it, a shot in the dark, but possibly epoxy

MrCrowley wrote:possibly epoxy

possibly

I've made that sort of join before, like here for example. It's a minor construction detail. I'm more concerned with issues like bolt friction and spring strength.

edit: I was having a browse through the archives, not surprisingly similar ideas (this too) have been proposed before, but it doesn't seem anyone has managed to make them work.