Here's the full gun.
The issue with making the SNAP pump action is the catch placement. Because the catch on a +bow is on the plunger rod, the catch plate, and thus the handle and trigger, are farther back. This leaves enough room for the pump grip to slide back and forth. The clothespin trigger on a snap catches on the plunger head, which puts the trigger too close to the gun. To solve this, I simply made the pump grip extend beyond the front of the plunger tube.
The pump grip is 1.5 inch thinwall PVC that I snagged from Zach (Venom). The coupler is there because his pieces weren't long enough, so I stuck two together. I'm looking into other ways to make the pump grip, because I would like to use something that people have easier access to. Because the grip has to extend past the barrel coupler, we need to shave the edge of the coupler down to fit inside the pipe.
I then wrapped the coupler in clear packing tape and gooped it in. I used packing tape instead of e-tape because e-tape is really narrow, which means there's a good chance that the coupler would be crooked, and packing tape has an extremely consistent thickness of 0.003 inches. Just to be on the safe side, I drilled a 1/8 hole through the coupler and chopped off a hunk of 1/8 inch steel rod and made a retaining pin. This also serves as a dart stop.
Remember, the grip has to slide over this, so don't use a screw or a bolt, or anything that will protrude from the side of the plunger tube. Now you're going to want to make your plunger head.
I used the preeminent plunger head, but I swapped out the narrow bolt and wing nut for a 1/4 inch bolt and nylon locknut. I used a 1/4 inch bolt because the ID of all the washers I used for the head were 1/4 inches, so everything is automatically perfectly centered. I also used a retaining pin to hold the plunger head together instead of a screw because I didn't want anything mucking with the catch pin. Let's take a look at all the internals laid out.
There you can see the similarities in the plunger head and wire priming mechanism between the PumpSnap and the Supa Snap. I didn't have a u-bolt that was small enough to fit inside the spring so I had to put it at the end. This puts a LOT of stress on the bolt, so I just covered it in locktite epoxy putty. There is simply a bolt that goes through the back of the pump grip, through the wire priming mechanism, and is fastened with a nylon locknut. This pulls the wire back, and is able to slide forward while the blaster is primed. The stock is simply a pvc T shoved onto the 1.25 inch pvc body. Next, we have the endcap. Normally on the back of the blaster and secured with screws, ours must be in the middle of the blaster and cannot be held in with anything that protrudes out from the 1.25 pvc. Thus, we use another retaining pin.
This does not go through the endcap, rather, it sits behind it and simply keeps it from shooting out the back of the gun. All that's left is to construct your clothespin trigger and handle. Keep in mind, it needs to be fairly narrow, and you must have space for it in whatever you use for the pump grip/sleeve. I went with a fairly janky looking handle so that I could have it done in time for ILFF. I must say, it worked beautifully. I used this gun in every round that day, except for the cqb round.
Ranges are average snapbow ranges.
Edited by Stark, 05 August 2010 - 09:00 PM.