SpudFiles

This is an idea for a shell loading semi automatic I will tentatively call it my own, but if I am wrong speak up. I came up with this idea from looking at the various semi auto designs on this site and this is the product of my interest in a design that would lessen the lose of pressure inside the barrel itself. The one red blue and green pipes in the pic have to fit together snugly to prevent pressure loss, any ideas on how to do this would be appreciated.
The diagrams should give you a pretty clear idea of how it works, but I will explain anyways. The cycle starts when the shot is fired and the spring pulls the breech loading mechanism back into the open position. The spent round falls out and the end of the next round is forced in. As the air builds up in the chamber the breech slides forward and the next round is forced in through the slot at the bottom of the magazine. The reason for the slot is so the new shell won't immediately fly out with the spent one. Any suggestions, critiques or questions are welcome. thanks!
Now the pics (I hope):

i see how it works and i think its a good idea, but it would take lots of work to get working properly, especially if you don't have a good machine shop.

If your tolerances and craftsmanship weren't great you could expect serious jamming/catastrophe

If you can get this to work, it would be awesome (note the big "if")

You would also have to make it with a fairly small sized chamber, otherwise the reload mechanism would take a while before it worked (pressure buildup time)

In "semi-auto step 1" I can find one small flaw. That is that because the loading is spring fed, whilst the one is falling down into the barrel, the next one will also be pushed down, and cause a jam. This can be sorted with a gravity feed magazine (i.e. just take the spring out) Or by putting a small piece of >insert-suitable-material< jutting out to stop it. But then the jutting out piece will cause another jam in the next reload!
Maybe, if your cartridges are perfect size, this wont happen though

Otherwise, I like the design and I think it has potential, if you willing to be patient!

Alright, thanks for your feedback. I am hardly a great craftsman and my power tool collection consists of a cordless drill, a jigsaw and a dremel tool, so maybe a different project would be best. I might try it anyway, just for something to do (I might find a better idea in the process ) The main problem I would have is the pipe fitting snugly over the other pipes. That's probably where a lathe might be useful (maybe not). Thanks for the info Spud Yeti, I see what you mean.

Since your bolt is controlled by the air in the chamber, won't when you fire the gun the bolt will move backards releasing the shell and the projectile won't be able to go down the barrel?

That could be the case, I have zip experience with semi autos before this one, but my thinking would be that by the time the spring had managed to push the whole magazine back into the loading position, the projectile will be long gone.

Interesting thoughts, though somewhat overly complex if you don't have the right worshop facilities - with a bit of though, you could combine it with this blow-forward valve concept and simplify the process while keeping the basic idea.

This could work, but I think you would need a compressor that has a constant output of 100+ psi to get it going back and forth fast enough.

Good idea though.

My advise, for the pieces that need tight tolerances cut to about ¼-1/8 of an inch to were you need it the use fine grit sandpaper to get it finished, and don’t use the Dremel for reaming, it removes to much material with to much heat, go to Big Lots and get a $50 drill press and run it at a lower speed.

Big lots sells drill presses?no way?I thought they only sold grocery stuff junk

I might end up making a different type of breech loading mechanism, it seems here that I have bitten of maybe more than I can chew. (I have built only two pneumatics and one combustion so far).

-jackssmirkingrevenge- I could try to make that combination, but one of my design goals was to reduce if not eliminate any factor that would limit the air flow behind the projectile. It could be that I start with that semi auto design like the one you posted, and then gradually work my way towards my own design.

-Spedy- I am about to buy an air compressor, and I am looking at an 8 gal.125 psi max pressure model, I think that is as far as I want to go in that area, I only have so much money and space.

-judgment_arms- I assume by "pieces" you mean pipe (is that right?), anyway, 1/4"- 1/8" is a lot to sand of off anything, and I only have so much patience. I had no idea you could buy a $50 drill press, and I assume this would be for cutting the shell entrance/exit holes. As you can probably tell, I have not put a ton of thought into the physical construction of this design.

Frankrede, yeah, Big Lots has drill presses, but as I think about the price it may be closer to $75.
Hold up, I meant Odd Lots, sorry guys for the confusion…
But yeah my dad has one that was my great grandpa’s; the only thing wrong with it is the starter capacitor, it still runs, you just have to hand start it.

Kablooie, by “pieces” I meant all the parts the mash with other parts that must be custom fabricated. Especially any reaming that must be done.
And by ¼-1/8” I simply meant that you need to get it close with a machine, and do the final fitting by hand, especially when it comes to reaming.

The drill press would be used for every thing from drilling holes for pivot points (if there is any) to sanding and reaming. I recommend using a sanding drum for reaming and a belt sander or just a piece of 80grit sand paper for rough turning or reducing the OD of pipe.

Also get a good high carbon steel pocket knife; I use my Swiss Army Knife more than another tool. When you get one make sure it’s got a blade about ½” wide as that width makes it perfect for reaming and that it doesn’t say “CHINA STAINLESS” anywhere on it.

judgment_arms- What's Odd lots? Is there really a place with that name? If I do buy one of these tools, what would be the best investment (for this project as well as future spudgun projects)? I see what you mean now about the sanding. I do have a pocket knife, it says "Swiss Stainless" on it so it should be fine. Thanks!

Kablooie, you live in the states? If not that may explain it.
But if you do live in the states just look in the “old” part of town; that’s generally were you’ll find ’em. I know they’re in Ohio, Arkansas, and North Carolina, I assume they’re in other places as well.


You best investment would be a pack of sand paper because you’d be shelling out the least amount of money:).
But seriously, get your self a cheap drill press and a good sanding drum, a good “plastic pipe” saw, a set of files and rasps, a table vise, sand paper, and a square.
That’s about all I use, you may want a good belt sander but that’s optional.

When it comes to your knife, get a good Arkansas stone and put an edge sharp enough to shave with on it, otherwise it ketches and leaves the surface rough, and keep it sharp to.

Oh and as for the price of the drill press, I’m 88% positive that it’s about fifty bucks, and comes with a deck vise!

EDIT: it’s BIG Lots, not ODD Lots, I had it right the first time… sorry for the confusion.