SpudFiles

I'm in the middle of designing a semi auto pneumatic gun and to do so, I was considering using a blow-forward bolt but after looking over several diagrams and pictures, it seems this might decrease the speed of each shot. I'm not sure if this is true or not, so if there's anyone who has made one, or anyone who may have alternative ways to automatically reload, I'd love some feedback

As some of the air is used to move the bolt, inevitably there will be some power loss.

If you want to avoid this, you can look into a system similar to the one used by the FX semi autos where the "waste" air escaping the muzzle after the projectile has exited drives the reload mechanism.

Interesting. can you post a link?

I have also been looking into a way to connect my air tank to a hopper, but in my design, it seems my golf ball would fall down before the gun could shoot.

Here's the patent for the FX Revolution:

http://www.google.com/patents/US2006027 ... on&f=false

There's also the Monsoon, this is mine taken apart



Here's a design based on a similar concept I had dreamt up a while ago, haven't actually made it though:



This one uses cartridges but you can make it much simpler with a bolt instead.

If i could get something like that to work, it would look so sick!
what psi does that use?

The Monsoon doesn't cycle below 1500 psi... but then again, it not only has to load the pellet but also cock a substantial hammer spring. If you're only moving a small reloading bolt, you should be able to get away with much less.

Much less meaning sub-100? Like 80 or 90?

You would have to make sure enough air is available if you're running at low pressures, this means a relatively large chamber volume, and the piston at the muzzle would have to be large diameter.

I'm not feeling to confident in this idea for my gun. I'm sure it'd be much more practical with other builds that use higher pressure. I still think a blow-forward bolt would probably be my best bet.

I've always wanted to make a prototype using low pressure, too many projects on my bench at the moment though.

I know what you mean. If you ever do get around to it, I'd love to see how it works!

In my airsoft semi, the reload mechanism is connected to the piston in the main valve itself. I know another member has copied the design for firing marbles.
If I were to build it again, I'd try to use a spring between the piston and the reload mechanism, instead of a solid rod - the piston generates lots of force and I've broken one bolt when it jammed on a BB. For larger calibers, the tolerances would be better.
Linky: http://www.spudfiles.com/forums/semi-au ... t1007.html

My idea for a gas operated design, or really any design using intermittent, explosive force, would be to let the force cock a spring, and then use the force of the returning spring for actuating the reloading mechanism. This way the force is predictable, and can be slowed down as much as necessary.

have also been looking into a way to connect my air tank to a hopper, but in my design, it seems my golf ball would fall down before the gun could shoot.

Ah...so it's golfballs you plan to use...

In that case you will be consuming gas pretty fast.
Seems like Poland Spud's semi design is the way to go then.

Look it up.

His design used the rising chamber pressure and the pressuredrop after the shot ...to load a round.
That means there is no loss in power during the shot itself.