This is a prop that is actually very easy to make. Mine is based off of Jack's laspistol, with a few changes. Since there are thousands of variations of laspistol in the 40k universe, you can often use readily available parts.
I used the same base gun (seen below) as Jack and more or less followed his procedure. The first thing I did was to disassamble the gun. I simply cut the tip of the barrel off, where a plastic ring was glues on, and unscrewed the halves. The only internal part I kept was the trigger. Following Jack's photos, I cut out a battery hatch in the grip, trying to keep the cut as clean as possible. With the gun in halves, we have to remove the barrel. This is actually very easily done, as the inside of the each half has a flange you can guide your saw with.
Images from Imperial Toy Corporation.
With the gun chopped up, we can start rebuilding. From this point on, I did my own thing, diverging from the overall look of Jack's. With the two halves screwed back together, the grip slides around, and need to be fixed. To do this, but allow the halves to still be disassembled, I first took off the slide. I then mixed up some Devco Plastic Welder and added a few blobs to the inside of each slide half, being sure that there is no chance of fusing the slide halves together. Then I simply assembled the slide and gun, with the slide in the right spot, and set it aside to cure.
The barrel was the next thing to design. My final barrel assembly consists of a hard plastic tube, a superglue container, O-rings, a film canister, and a cardboard tube. The plastic tube is from a squirt gun pump, and the cardboard tube is from the grocer; it's the tube that plastic produce bags are on. I should note that I chose these bitz because they fit together well. I wedged the superglue container, bottom end first, into the plastic tube. I did this because it strengthens the barrel, and I can keep it centered. In the gun, there are already holes molded in along the barrel centerline. The wedge tip of the superglue container presses into one of these, centering one point. The take care of the other point, I turned to my Unibit. The hard plastic tube is roughly 11/16" on its outside diameter, and the Unibit happens to have a matching dimension. I drilled out the hole on the front of the gun, and the final result is a pair of holes that the barrel assembly is centered in. Also, this should help me mount the laser pointer later on.
For the "emitter" on the end of the barrel, Jack used a camera part. There was no way I would be able to find that exact part, so he suggested a film canister. A sloped cut was needed on the end of the canister, but this was difficult to do, as the canister would deform, ruining the cut. I searched around in my bitz for something rigid that would fit snugly into the canister; this is where the cardboard tube comes in. The tube fits tightly inside, and is very rigid. Not only that, but the hard plastic tube fits nicely inside; see where I'm going? Using my miter box, I cut a 45° angle in the canister/tube assembly. I originally planned to just toss the cardboard, but after I saw that it fit nicely onto the barrel, I kept it. I just cut an extra bit off the end to set it down into the canister slightly, giving me a nice detail. Using my Unibit again, I drilled out the bottom of the canister to fit the barrel. A clear peice of plastic will be installed into the "emitter" after paint. A suitable number of O-rings fill the space between the front of the gun body and the back of the "emitter."
Instead of doing the handgrip like Jack, I decided on doing a box to simulate a powercell/clip. I just built a box out of plasticard to fit over the front of the gun body, removing details on the gun body were needed. The assembly as it stands now can be seem below.
From here, I am going to install the electronics and laserpointer into the gun body, which is why none of these parts have been glued together yet. I will build a "scope" from PVC pipe and fittings, and some clear plastic domes. Other greeblies will be added for some additional detail, epoxy putty will clean up seams, and the thing will be painted.