After several experiments with repair couplings and other things, I fell back to my first homemade writeup for inspiration. Instead of looking for a preassembled chamber, I would modify my earlier design of the piston inside the B.U.F.F. for better sealing. That, combined with an amazingly easy to open ball valve, made for a blaster with lots of power.
1 1/4" PVC
1" to 1/2" PVC bushing
1 1/4" PVC tee
1/2" PVC tee (with the tee off threaded)
1/2" Sch. 80 PVC ball valve made by KBI
(2) 3/4" PVC caps, with large hexagonal ends (made by Genova?)
3/4" PVC coupling
(2) AS568A-216 o-rings (1 1/8" ID, 1 3/8" OD)
Your choice of skirt seal/superlative plunger head/etc. Look them up.
(3) 3/4" PVC caps
(2) Hillman #49 springs
Whatever pump you choose, and the fittings required to convert to 1/2" Male threaded PVC
Here's the new version of the internal piston. Under ideal construction, you would use a 3/4" coupling, and 2 3/4" plugs. Specifically, the kind with large hexagonal ends that you can shave down to fit ever so loosely into 1 1/4" PVC. In a nod to overengineering, I went ahead and added a skirt seal to the side that faces the barrel. Normally, I'd use polycarb circles and McMaster skirts, but none were handy. I improvised and took the skirt seal from a broken Marshmallow blaster, which fits perfectly in the 1 1/4" pipe.
Now we can place springs behind it. I used 3/4" PVC caps to keep the springs lined up to minimize issues. Pictured are Hillman #49 springs. Since then, I've nested other random springs inside the #49s. a 1 1/4" PVC tee will cap the back of the blaster, acting as the spring rest and the shoulder stock.
The main work is done. I capped the frot of the chamber with a 1" to 1/2" bushing (with a wrap of tape and JB weld). The bottom of the tee is threaded, allowing use of the Dual Action pumps from my Modular Air Gun System. on the front is a KBI 1/2" Sch. 80 PVC ball valve. Aside from the initial opening force, it is amazingly easy to open all the way - the result being performance like the spring-loaded ball valves in some Super Soakers. I'll throw a longer handle on there, so that I can use the bike pump as the grip and have a normal trigger.
Ranges? I'm still testing, and improving. There's currently no lube (need to do that ASAP), but it's sealing perfectly. 10 pumps fully compresses the springs, and firing is the most amazing sound I've heard from a homemade blaster yet. With a 2' CPVC barrel (hardly the best barrel material for airguns), I'm breaking 120', and there's STILL extra power available for a longer barrel. Needless to say, I think I have the design down pat.
UPDATE: My design allows for disassembly from the backside. Which means different spring combos. You can use a spacer to replace your extra springs!
Currently, the reduced volume and springs brings the ranges within reason. Still 100+, but similar to other homemade primaries. And I only need 5 pumps now; the UBER version needed 10 for full spring compression (and amazing power).
There are several issues to deal with:
-SHEER POWER. I was aiming for this kind of power; however, aside from a massive shotgun or rocket launcher, it has little nerf war use. Make it smaller, with one smaller but stiff spring (or precompressed spring, if for some reason, you only have a [k26] laying around...)
-OPV. There currently is none. I'm looking at the possibility of placing a tiny hole in the 1 1/4" PVC pipe. Presumably, once you've filled the chamber enough to pass that hole, it will bleed out, and the spring will seal it off again.
-Plunger padding: I need to do this ASAP, as there is a ton of force being applied. You will have to do it as well.
Questions/comments/flames can now proceed.
Edited by Buffdaddy, 20 August 2011 - 11:12 PM.