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Need Help - Converting a large pneu to handheld.

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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Need Help - Converting a large pneu to handheld.

Unread postAuthor: Pete Zaria » Sat Oct 02, 2010 6:49 pm

Thanks in advance to anyone who might take a few minutes to answer a couple of questions for me.

Background:
A couple of summers ago, I build a large pneumatic with a 10' stick of 4" PVC for chamber and 10' of 1.5"SDR21 sleeved in 2"SCH80 for barrel, over-under style. It was massive, hard to move around, and blew large holes in treestumps etc... with golf balls.

However, because it's so massive, it mostly sat in storage, hanging from the rafters of my garage. I decided to cut it down to hand-held size so that I can use it more frequently.

I built it reasonably modular; the "manifold" section (with valve, etc...) detaches from both chamber and barrel; that's the good news.

Here's the manifold:
Image

All parts Sch40 NSF-PW rated. Spray-painted black with Krylon.
1. Fill valve and air compressor quick connect
2. Pressure gauge
3. Safety valve (must be closed for pilot volume to be exhausted)
4. 2" Union, connects to Air Chamber
5. 2" Rainbird sprinkler valve, solenoid removed and hole enlarged
6. Nylon T in "pilot volume" which connects to Blowgun (pilot valve)
7. Modded blowgun pilot valve
8. 2" female threaded coupler to connect to barrel

I'm planning on cutting the 10', 4" air chamber down to 3 or 4 feet, leaving the U bend (actually two 90' fittings) and 4"-2" reducer (to connect to the union, #4 in diagram) intact. On the other end of the chamber, I hope I can re-use the 4" PVC end cap by carefully dremeling out the old pipe stub, as 4" PVC end caps are expensive in my location.
I'll cut down the barrel to about 4 or 5 feet and otherwise leave it intact.
I'm a reasonably big guy at 6'0 / 190 so I think this size will be manageable.

The hose connecting the sprinkler valve to the blowgun will be shortened to just a few inches, which will drastically reduce pilot volume. I'll also try to find a larger T fitting (#6).

My questions:

Any advise on how to dremel out the pipe stub from the 4" end cap so that it can be re-used?

Does anyone have any suggestions on which way to orient the manifold section relative to the barrel/chamber?

How about where to locate the "handles"?

Any ideas on a "spacer" to hold the barrel and chamber together, parallel? Previously I've used a wooden block and hose clamp, but would like something more professional.

Any ideas for an on-the-cheap golf ball breech loader?

Thanks for your time,

Peace,
Pete Zaria.
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Unread postAuthor: Gun Freak » Sat Oct 02, 2010 6:58 pm

For the endcap thing, are couplings as expensive as the caps because you could just leave a few inches of pipe sticking out of the cap and stick a coupling on.
For a breech, use a stick of 2" sch 80 over the barrel and put a hole in the barrel the size of a golf ball, and slide the pipe back and forth to open and close it.
For the spacer, a wooden one can be made to look cool but one made out of PVC fittings would look better in my mind if you spent a little time on one.
For handles, pick up the cannon like you normally would and put your hands where you want the handles. Mark those spots and then just attach handles, I think that is what you're asking.
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Unread postAuthor: jackssmirkingrevenge » Sun Oct 03, 2010 12:29 pm

How about something like the Barrett M82A2?

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Unread postAuthor: Fnord » Sun Oct 03, 2010 1:25 pm

I'd also suggest using a coupling if possible. I don't think there's an easy way to dremel out the stub. You could try softening it in the oven(pre-heat to 325) and pealing the pipe out, but I imagine the solvent weld is nearly as strong as the actual pipe.

If it were me, I'd would have set it up this way:
Chamber> Reducer> 2"tee > Valve > 2 Elbows > Barrel. This would be an under/over config with a lot more room for a barrel than you have right now.

A good spacer can be made with wood and a hose clamp; just wrap it with a strip of rubber to hide the clamp, and paint. If you want it permanent, use some bondo or fiberglass to cover the clamp.

Handles: It's a bit big to shoulder, so maybe arrange the handles like a hip shooter- rear grip above and inline with the barrel, front grip above and crossing the barrel. The gun's center of gravity should be roughly halfway between them.
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Unread postAuthor: Pete Zaria » Sun Oct 03, 2010 2:46 pm

@GunFreak:

Good idea on the coupler for the chamber pipe, that will probably work. I'll check and see how much they are next time I go by the plumbing supply spot.
I don't like the idea of sliding 2" sch80 over the 1.5" SDR21 for a breech loader - it would leak like mad and reduce the amount of air driving the golf ball. I'm leaning towards a repair coupling, or some cam-lock fittings with the stops dremeled out (so the barrel can pass-through the cam lock).

@JSR:

That's kind of what I was thinking... I'm leaning towards using pipe saddles to attach handles onto the bottom of the gun, probably one on the chamber and one on the "manifold" between the 2" T and sprinkler valve. I'll use 1.5" pipe for the handles and mount the blowgun inside the rear handle as a trigger.

@Fnord:
I like your idea for configuration, the only problem is, I'd have to buy the two, 2" 90 degree fittings and 4"-2" reducer bushing and coupler, since the ones used in the 10 foot configuration are solvent welded onto the chamber end. Otherwise, I'd go that route for sure, and I may do so in the future, but for right now, I'm going to go the low-budget route and work with as many of the parts I already have as possible.

Good idea on the spacer, I'll give that a whack and see how it looks.

On handles: I'd rather shoulder fire it, for accuracy reasons, and I'm a pretty big dude so I don't think the size will be a big problem.

Thanks for the input everyone, I'll post back when I have some time to work on it.

Peace,
Pete Zaria.
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Unread postAuthor: Gun Freak » Sun Oct 03, 2010 4:56 pm

Cam locks work very well. But aren't they kind of expensive? One guy from our sponsors made a GB cannon with the sch 80 breech load and he said that he feels little to no air being lost by the breech.
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Unread postAuthor: HellenKeller » Sun Oct 03, 2010 5:45 pm

I see you deleted my comment. YOU SAD? boo hoo crybabay noob.
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