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Development of a breech design

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Development of a breech design

Unread postAuthor: Blitz » Sat Apr 07, 2007 2:46 am

Hi there, I'm a long-time watcher, first time poster -- I just couldn't resist getting back in the fray of spudguns after being inactive for over 5 years.

Anyway, I've looked through the pneumatic cannon database and saw pretty much every entry made. Most of the guns which aren't muzzle-loading seem to be loaded via a bolt-action design, with some exceptions.

The majority of my larger cannons are over-under designs, for the sake of space. If any of you remember Joel's Mega-Launcher, he had a threaded end-cap on a cross, opposite of the barrel, where ammo's loaded. Air comes in the two sides perpendicular to the barrel/cap.

Instead of screwing the cap on, I wanted to design a breech that somewhat emulates the breech of real artillery; with a hinged plug that'd seal against the very rear of the breech for quick loading and firing. Although I feel this could allow larger cannons to be fired more quickly, it's more of a proof of concept than anything since many larger cannons take a while to refill the air chambers. Think of those air-tight jars with the hinged lid and either a nylon or rubber o-ring to make the seal.

So, I wanted to adopt this concept. Since my cannon testbed is a typical over/under with no barrel at the moment (with a 2" QEV that bends at a 90 degere angle, and is attached directly to my tank), I plan on attaching my 3" barrel piece directly to a 3" Tee, with the 90 degree connection going to the valve (with a 3" to 2" bushing somewhere in there). The unused end would of course be my breech. Again, this is just a proof of concept and for my own development as I start using larger-diameter barrels. Breech-loading bean cans in this manner could be incredibly convienent!

Has anyone tried this with any success?
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Unread postAuthor: jrrdw » Sat Apr 07, 2007 5:39 am

No, i certinly havent tryed this. Who could forget Joel's Mega Launcher. I know exactly the jars your talking about, but the wire set up would totaly have to be overhauled. I'm thinking maby a well cap design??? But with a quick release instead of 10 screws, i'm not sure if they would hold pressure either, but ours has a nice looking seal on it. Maby theres a seal for your idea. Fasten a tightly made gate lock, drop lever in a grove set up. My well sleave is 6" though, do they make them caps smaller??? I'll keep my eye out in my travles for this idea, it's a good one.
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Unread postAuthor: FiveseveN » Sat Apr 07, 2007 6:51 pm

How about a ball valve or cam lever coupling instead of the hinged plug? With the coupling, you could incorporate a ramrod into the removable part, which makes the loading process even faster.
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Unread postAuthor: Blitz » Sat Apr 07, 2007 7:22 pm

I think a large ball-valve would be more feasable, but I didn't want the overall length to be much more than 2-3 inches. But with a ramrod, it wouldn't be so bad; so I'll just have to load like large-caliber naval artillery. :)

However, I'm going to try the coupling as well, and see how that feels. I can just cut a ~2-3" piece of pipe and solvent-weld that to the rear of the tee and give that a try. I presume you mean the coupler is sealed on one end, right?
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Unread postAuthor: VH_man » Sat Apr 07, 2007 7:44 pm

What i personally think you should do is line the rear of the cap area (dont know what to call it) with neoprene. to replace the breech cap, siply get a peice of PVC sheeting and hinge it to the back of the barrel. on the other side put some kind of clamp lock like on those airtight glass jars used to store yeast..... sorry if you dont get what im talking aobut but i really want to see this...... should be pretty sweet. O and BTW the pressures in a pneumatics barrel only reach about 50 PSI..........
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Unread postAuthor: Blitz » Sun Apr 08, 2007 1:27 am

Yeah I would too, because when I apply it to my 4" barrels I plan on making shell casings and it'd actually be kinda cool to have it fall out of the breech when I pop it open after a shot. :)

At this time, I don't have a working digital camera but I plan on getting one sometime, probably after my wedding in 3 months. But maybe I'll borrow someone else's.

VH_man: that's pretty much what I was thinking at the beginning... But I would use the open end of the cap to go against the back of the tee. I could just make an O-ring or something and apply it to the rim of the cap. I wouldn't trust a piece of PVC sheeting to handle the initial rush of air from the chamber, though.

Then, I have to consider how I'd secure the cap to the tee via a hinge, and what I will use as a locking mechanism. Shouldn't be too hard. Time to get busy, I'll check in with this thread in a few days and give an update of my progress. I think I have a few of my own ideas, but I wanna try them out first.
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Unread postAuthor: goose_man » Sun Apr 08, 2007 7:02 am

I saw on spudtech a while back a brilliant design for a breech-loading mechanism. It's a ball valve with a hole drilled in the side while the ball valve is is the closed position. Essentially, to load the ammo, you put the valve in the closed position and insert the ammo through the side hole into the rotating ball part of the valve. Then you open the valve and the ammo is now able to go forward into the barrel when you fire. No air escapes because the sides of the rotating ball are still intact, and a ball valve is manufactured to not allow air to escape.

Personally, after I drill my hole in the side of the ball valve (for me it's 1/2"), I glue a sleeve into the rotating ball that has an inner lip on the back end to prevent the ammo from moving backwards. I then insert a sleeve with the same inner diameter into the barrel so it lines up with the ball valve's sleeve. This design works very well for my 1/2" steel ball bearings, however I'm not sure how it would scale up if you wanted a larger barrel.

Being as I cannot access spudtech, I cannot give credit to whoever it was that came up with this, because I forget who it was. If you remember, or it was you, please give/claim proper credit. Hope this helps!
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Unread postAuthor: paddo » Sun Apr 08, 2007 7:34 am

thats a really good idea. and its giving me really good ideas.
i pm'd you just before.

i like this idea im going to HAVE to try it very soon. thanks for a bit of inspiration.
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