I`ve been wanting to build a good spring powered pistol for a long while now. I gave it a go a while back with rubber bands as the propulsive force and had limited success. With that pistol though I was working within a constrained space to keep a 1:1 scale to typical handgun proportions. After that I realized that to build a plunger based pistol would require a reasonably long gun.
The other night I was watching Equilibrium for the 1457th time and it dawned on me to model a homemade after the Grammaton's modified 92s. The long barrel made for a long frame that I could pack a long enough plunger into to get good performance. Below is a image of the Grammaton Berretta 92 from the movie.
And here is my PVC incarnation of it.
I dub it the Grammaton Nerf Sidearm or 'GNS' for short
So, you’re probably saying "enough already, show me the guts". Well here you go.
There is no new technology in this pistol. Basically it is just a nitefinder built out of PVC. It uses the same type of catch and trigger mechanism that you find in every Nerf Brand spring gun. It’s about as simple as you can get and it was pretty easy to craft out of every day supplies. Like most of my other homemades, this pistol is made out of mostly PVC, some balsa for non-loadbearing endcaps, and music wire. I introduced aluminum for the trigger plate. This piece was pretty complex and had to take a large compressive force so metal seemed to be the logical choice. Like the FAR the GNS is assembled with screws allowing it to be fully disassembled with just a screwdriver.
Component Description
Frame
Similar to a real handgun the pistol grip, trigger guard, and lower part of the frame are all one piece. The trigger mechanism is attached to the upper portion of the frame rather than the lower. The lower portion just covers the mechanism. The pistol grip is made in the traditional manner. The trigger guard is 1" PVC sections. To strengthen the trigger guard I embedded music wire at the corner and where the trigger guard meets the frame as well as glueing it.
Plunger
Like the FAR, the plunger is made from a 1/2" endcap and uses 1 19/16" O-ring instead of the FAR's 2. I was cramped for longitudinal space and gave up the redundant O-ring. The plunger rides in 1" thin walled PVC like the FAR as well but the plunger shaft is 1/2" CPVC. The slot on top of the plunger is engaged by a screw through the receiver and prevents the shaft from turning. The catch hole in the plunger needs to face down at all times. The catch hole can be just seen at the front of the guide slot. the actch hole is made from a piece of brass tubing that goes all the way trhough the plunger shaft. The catch engages the plunger from the bottom. I made a loop out of music wire that attached to the rear of the plunger for cocking.
The spring is a AR15 carbine spring with about a third cut off. When retracted the spring is fully compressed. When installed in the gun the spring is compressed about 25% of its free length.
Barrel
The barrel pulls out of the gun as a unit and is interchangeable. The one currently in the gun is a crayola barrel nested in 1/2" PVC. I plan on making another unit with a 1/2" CPVC barrel. the barrel is secured in the receiver with 3 screws placed radially around the rear and a single screw in the front. The barrel assembly adsorbs the shock from the plunger so I wanted to be sure that the barrel was not going to launch out of the front of the gun.
Trigger Mechanism
The trigger mechanism is just like what you would find in a nitefinder or crossbow. As seen above the plunger shaft has a catch hole in it. A sprung catch it located on the underside of the receier and engages the plunger shaft as the plunger is retracted.
The catch is made of music wire and a cut pen spring is used to provide the upward force. The trigger plate is made from 1/16" Aluminum. It rides is a channel made from two slivers of PVC. The ramped sectionon the right side of the alminum piece is what depresses the catch to release the plunger. The slot in the trigger plate is engaged by the U-shaped piece of music wire to retain the trigger and restrict its motion to purely linear. The trigger itself is made of PVC and attaches to the trigger plate with a pin. The trigger must be removable for the gun to come apart. The large spring pulls the trigger back forward. The below pictures show how the trigger goes together.
Performance
I am extremely impressed with the performance of this pistol. With stock micros it gets about 70-80 feet. That’s with the crayola barrel. Using stefans gains a little range. I`ve gotten 90’ with a tight Stefan. The feel and weight of the pistol is good. It’s very balanced and easy to aim.
I`ll likely do a writeup for this pistol similar to the writeup for the FAR for Nerfhaven. I`ll have a schematic up soon like the one for the FAR and I also might finish up the CAD model as well. This pistol wasn`t that hard to build. There aren`t really any ultra complicated components. The trigger plate is the most complex piece but it's not that bad. It jsut takes some time with a dremel.
VIDEOS!!!
Firing-1 <1.3Mb>
Firing-2 <0.8Mb>
Edited by boltsniper, 05 October 2005 - 08:56 PM.
