SpudFiles

2" x 18" chamber
.75" x 16" barrel
2", 5.5oz piston made of steel and PVC (see description below)
Pilot valve: 3/4" QEV with 3/8" ball valve as its pilot



So it's nothing remarkable, I was just happy I cut down on pilot volume by replacing my home-made 2" to 3/4" reducing bushing (the white one in the picture) with a one-piece bushing, shown below it. I also replaced the crappy blowgun with a 3/8" ball valve. Performance from these two upgrades made it quite peppy at 90psi. At 200PSI it just hurts my ears...

Believe it or not, the gun's two years old - - I just forgot to post it last year when I got it to work. Piston is made from two 2" steel washers, a 1.25" coupling placed between them, and two neoprene washers on each side (one as the sealing face and the other as a bumper). It weighs about 5.5oz, and making it lighter didn't seem to affect performance so I left it as-is.

You probably figured it out already, but the threaded street elbow on the QEV serves two purposes -- one, for directing the pilot exhaust valve air away from me if desired. And two, I put my hand over it when I fill up (since I fill from the chamber, not the pilot valve. I did this to minimize unecessary plumbing in the pilot). The threading in the front is for me to be able to remove the barrel and bushing it's housed in so I can either change hte barrel diameter or service the chamber. The threading in the rear is probably obvious to the rest of you -- piston service. I will be adding o-rings on the both of these threaded areas to improve air tightness (although there's no leakage right now).

And yes, I know I definitely need to clean it up. I had planned on painting it as well, and adding o-rings to the two threaded areas of the chamber. Believe it or not, the barrel is not glued in the bushing whatsoever, it's force fitted. I may end up reinforcing it, but even at 200PSI the piston hasn't pushed it out at all so far. I may replace the barrel with a sch80 version and toss in a paintball, just to see what happens.

I'll get damage pics/videos up sometime later this week or next.

Nice gun! Is it a 2 fill gun? You fill air behind the piston than in the chamber itself?

Nah, it just goes in the chamber directly. The QEV is why I put my hand on the exhaust until the chamber hits 20psi, then I can let go. Otherwise the diaphragm won't seal.

Did you have a press to use for pushing the barrel through the bushing? Will be glad to see the pics. Nice build.

Small? Sorry to tell you, but that coax isn't that small lol.

but still a very cool coax indeed. very uniform and neat, i love it.
price for parts total?

again, nice work. can't wait to see more

I did at first, but then I used a rubber mallet to get it to my desired length. If I end up replacing it with a 3/4" sch80 barrel, I will have it pressed in all the way.

price for parts total?

I guess for all retail, it'd be around $35. The only thing I actually bought was the 2" x 3/4" bushing, which was 4 bucks.

I love coaxials...make me feel all warm inside... Well they do for me I guess because it's such efficient use of space and makes for a gun that's easy for the shooter to manage.

Nice little unit there. I'm glad you explained the elbow in the back, I wasn't getting it's purpose at first.

You shootin' paintballs, marbles, all of the above? At 200 psi, I'm sure damage is quite significant for small bore.

not too bad.

i would consider a camo paint job and maybe a custom wooden handle? It would add some individuality to it and look bad ass lol

In all honesty I haven't shot anything of significance besides a lever arm which has a 3/4" diameter ball knob on the end. Everything else has been smaller with plastic bags used as wadding. I'm not a big fan of using wadding though, because I tend to push it beyond the barrel and into the chamber. lol Although, I could just put a small bolt through the rear of the barrel to prevent that.

jeez, pretty good performance from a "smallish" coax lol.

little package....big punch

I try to keep the pressure below 120psi, only because I don't trust the fittings all that well. And even at 120PSI, GGDT predicts only 102 ft/lbs of muzzle energy with a 3' barrel and a 1oz projectile so it's really not that powerful.

It looked like a double air fill cause the thing next to the gauge.. but that was before I read the description

Oh, yeah that's the standard schrader valve I inserted to allow fillups from smaller devices, otherwise I prefer quick-connect couplers.