SpudFiles

Have a look at this one I had built, allows you the potential for breech loading as well as upping the performance significantly on account of the zero pilot volume.

First things first: Hi, everyone. . . been lurking for a few weeks.

To business:
the piston/barrel seal in this design is a ROYAL pain. . . .

6 years ago, I built an all-metal (aluminum and steel) artillery-loading version of this idea, firing soda cans/tennis balls. (150PSI max, 10ft BBL, 8 rnds/minute sustained.)

it'll kill a cinder block in one hit at 50 yards/70psi; we're talking total demolition here. I sound like a hyena anytime I get it out.
The sound is fantastic, and the visual effect of the soda can bursting is really nice.

I'll have to dig to find photos (that was about 3 computers ago. . .)

there are refinements I'd like to make to simplify loading, etc-- time, always time.

were I you, I'd go get a $20 caliper (at least) from the local harbor freight, and look at what Parker, et. al. have to say about the "crush" required for various pressures vs o-ring section diameter before I got started. I know I scrapped a couple of parts before I did. . .

JSR, Did your gun end up looking (internally) like the drawing, because you're right, there is technically no pilot volume, but the air flow looks very restricted, I also don't see how you would potentially breach load it, unless the whole piston device moved backwards, and then you could only load pre-pressurization.

I do not really see how you would breach load that while keeping the parameters of the original gun, it would need much modification, although it is worth looking into...

By the way, how much pressure can a syringe hold safely?

that 1/2 inch pvc is actually 3/4 inch? and 3/4 inch pvc is 1"??

it's the same with malleable iron pipes... it is the so called nominal size..