Cpvc PistolSplat (Ps-800)
This is sort of a blast from the past. I first posted this to the LGLF blog in 2008 as a help to beginning nerfers so they could spend less time agonizing over mods and more time nerfing. Long story short, it's not on that blog any more, so I'm putting it up here. There will be a couple of other threads like this coming too.

Required Materials
Pistol Splat (can be found at Spencers or online):
Cpvc coupler
Cpvc
Total- about $15
Required Tools:
Screwdriver
Dremel
Hot glue gun
First, cut through the top and bottom of the red cap at the front with your Dremel. You will also have to cut through (or otherwise remove) the cap at the end of the feedport. Remove all screws in the side and open the blaster.
You will need to remove the gray piece in the middle that pivots, as well as the sliding piece at the front:

Pull out the plunger tube:

A spring may fall out when you do this. You can throw this away; it is only there to weaken the gun.
Put a layer of hot glue around one end rim of the cpvc coupler, and slap it onto the black end of your plunger tube. Making sure it’s centered and straight, add another thin layer of hot glue around the joint. Once that layer dries, put another. Layering like this adds tensile strength, making your mod last significantly longer.

Replace the plunger tube where you got from. If your cpvc coupler doesn’t fit nicely inside, you may have to sand down where it goes using the Dremel. The sizes of the couplers vary, but mine fit in well without needing any further modification.
Put the two halves of the blaster together, and replace all of the screws.

Cut a 4-5†piece of cpvc (if using stefans or converted dart tag darts; optimum length will vary. Experiment! Cpvc is cheap!) and push it into the coupler via the front.
You’re done! You should have a superb, primary worthy pistol at this point. It’s not the fastest or furthest shooting thing out there, but it beats out most, and it’s simple and reliable.
Some tips on use:
To load, pull out the cpvc, put a dart in the back, and place the barrel back into the coupler. To prime, pull the lever arm up and push it all the way down. And to fire of course, pull the trigger!
The gray piece from the center that we took out was the trigger lock. Do not dry fire the gun (fire the gun without a dart in the barrel). If you do prime the gun and need to unprime it, pull the lever all the way back, and pull the trigger. Then slowly lower the lever.
Do not store the gun loaded or primed. This will deform your dart and weaken your spring, respectively.