I used a Rainbow catch, up-sized to a 2" PVC OD.
My plunger rod is 5/8" OD PVC rod, with a piece of 1 3/8" x 5/8" polyethylene tubing, to attach the U-cup. The tubing isn't actually the correct specifications, on average about +0.15" on the outside and -0.15" on the inside. I drilled out the inside diameter with a 5/8/" bit so it would fit over my plunger rod. Since no actual tubing fits over the polyethylene, I just had to tape out some spacers to keep the U-cup in. A flap valve was installed in the top to prevent jams and vacuum feeding. I had to drill a hole through the center of the plunger rod for the air to escape behind the plunger head.
The pump action mechanism is closest to what SgNerf did with his blaster. There is a slot in the back half of the blaster, and another in the plunger rod. A bolt goes through both sides of the pump tube, which pushes back on the plunger rod. The slots allow you to return the pump grip to the front position after it's primed.
The pump tube is constructed of 2.5" PVC. It fits very nicely over 2" and is the closest sliding fit of any two sizes of PVC there is. The thing in the front is a cut down reducing tee that reduces from 2.5" down to 1 1/4" on the bottom. I'd honestly like this a bit smaller, but that's the smallest reduced tee they had. One nice thing about making Sgnerf's sytle pump action, you don't need to keep the back of the pump tube closed, like you would in a normal RBP. This means construction order is a lot more lenient because you don't have to put the pump grip on before the handle is attached.
All in all, I'm pretty pleased, although there are reason people don't use 2" as a PT. I ended up using 4" of draw, compared to 5.75" I'm using in the RBP Rev2s, so it's only about 5" shorter than a standard RBP. The thing also weighs a million pounds. You could seriously ruin someone with this. The priming action is pretty smooth, although there is some friction when the pump grip is all the way returned forward, most likely because my slots aren't perfectly straight. I'm going to have to experiment with barrels since the plunger rod is pretty heavy and moves much slower compared to a 1 1/4" PT springer. I will also most likely put a stronger spring in there to make up for the added plunger weight.
I know someone will ask, but ranges are bit hard to determine now. It's really windy outside and I know I don't have the proper barrel on this thing. Just from initial testing, ranges will most likely be similar to a 1 1/4" PT blaster with ~5.5" of draw.
Comments, questions? I'm sure I missed some stuff, but I wanted to get some discussion on this and larger PTs in general.
Edited by Ryan201821, 06 September 2011 - 04:16 PM.