All images and content © Evan Neblett 2006
GRAMMATON NERF SIDEARM (GNS)
Updated: 2/5/2006
I attempted a pistol a while back and BS-4 is the result of that endeavour. My main goal for that project was to keep the resulting handgun on a 1:1 scale with real handgun. That proved to be the down fall of BS-4. While performance was impressive for it's size and specs, it was still pathetic for a homemade. My desire to build a high power pistol was definitely not satisfied by BS-4 and I thought for a long while how to get good performance out of a pistol. It would have to be larger to accommodate a decent sized plunger. One day while watching Equilibrium for the 1000th time I got to thinking about the Grammaton pistols. Technically they are Beretta 92's, but they have substantial barrel extensions making the pistol quite long. Usually long pistols look unproportional but the Grammaton pistol doesn't. It actually looks pretty damn mean. That's when I decided to build a Nerf Grammaton pistol.
For the start I planned on this pistol being a spring/plunger gun. There were no plans for this pistol to have a magazine or anything of that sort. The pistol was to be loaded like any other Nerf gun, the the muzzle. The barrel needed to be only the length of a dart. The barrel ended up being about 3 inches long. The rest of the length of the pistol would be dedicated to the plunger. There were two big issues with BS-4. The plunger was much too short and there had to be a slot for the operating rod for the elastic bands. A spring would be used to eliminate the slot and maintain a sealed plunger shaft. I wanted the finished gun to be as close to proportionally correct as possible to the Grammaton pistols from the movie Equilibrium. I wasn`t too concerned with the scale as long as the proportions were correct.
Knowing the length of the barrel and the general shape desired. The plunger could be up to 7 inches long. This was more than adequate for decent performance. The barrel and plunger reside in a section of 1" thin walled PVC. To create the correct profile and to allow space for the fire control system, a section of SCH 40 1" PVC was ripped and positioned under the receiver. This created about 1/2" of space under the receiver. The catch and trigger setup for this pistol is very similar to the systems in most spring Nerf guns. The catch is a section of music wire that is sprung to keep a upward force on it to create positive engagement in the plunger. A wedge cut from aluminum moves along a track inline with the axis of the gun to depress the catch. This trigger plate is what the trigger is fixed to. A low stiffness spring keep the trigger at it's forward-most position at all times.
The pistol grip is fabricated in my standard method with 1" PVC. It is permanently bonded to the lower frame. The entire pistol is assembled with pins and screws and can be completely disassembled for cleaning or part replacement and maintenance.
Ordinary PVC piping is the main material used in the construction of the GNS. The sizes used are as follows:
1" 200 psi PVC (Receiver, Grip)
1/2" PVC Couplers (Barrel spacers, Plunger Head)
1/2" PVC (Barrel)
1/2" CPVC (Plunger Shaft)
Some other special PVC fittings were used in certain situations. For situations where a flat surface was required balsa sheeting was used. I use 1/8" sheeting and hand picked the hardest pieces for durability. I like balsa because it is easy to work worth, can be hard, and I have an abundance of it. To space the PVC pieces inside one another, I used electrical tape. This works extremely well and can produce extremely tight fits. I personally use CA glue (aka superglue) to due all the bonding involved. It adheres extremely well to both PVC and balsa. The advantage is the near instant drying time. CA will hold just as good as PVC cement. For assembly I used 1/2" #6 pan head sheet metal screws. These are just the right length to penetrate from the outside of the 1 1/4" PVC to the 1/2" PVC of the barrel but not penetrate the inner wall of the 1/2" PVC. They are very common and can be picked up at Walmart. The last major materials utilized in the GNS were music wire and brass tubing. These two were used in conjunction at all pivot points. Music wire was also utilized for retaining pins, pushrods, etc. See the materials list in the plans for a more detailed list of materials
The pistol can be completely taken down with just a Philips screwdriver. 1/2" pan head screws hold the entire gun together. In the places where a screw is not needed a pin is used, such as the trigger retainer and the trigger plate retainer.
Barrel
The barrel is probably the easiest component to fabricate out of the pistol. The bulk of the barrel assembly is a section of 1/2" PVC. Sections of 1/2" PVC coupler are placed at each end of the barrel to space it in the receiver and add bulk for screw mounting.
The 1/2" PVC is too large for use with micro darts which is what the pistol was intended to use. The prototype used a crayola barrel set inside the 1/2" PVC. On the Mk2 version, the crayola barrel was replaced with a tighter fitting 1/2" CPVC barrel. The barrel is fastened in the receiver with 4 1/2' pan head screws. Three screws are spaced radially around the rear barrel spacer. These three screws absorb the impact from the plunger and transfer it into the receiver. A fourth screw is placed through the front spacer to prevent play and further security.
Because the barrel is removable it can be interchanged with other barrel types. A threaded barrel can be manufactured and installed to allow the attachment of a suppressor. I have not gotten around to building this barrel assembly but I have collected the parts. A barrel sized to shoot mega darts could be installed as well for a higher caliber punch.
Plunger
The plunger was made as light as possible keep mass low. Lessons learned from the FAR proved that plunger mass had a large impact on plunger acceleration and resulting dart performance. A 1/2" endcap was used to make the plunger head. A groove was cut into the endcap and a #18 O-ring was placed in the groove. This created a good seal inside the 1" thin walled PVC. The plunger shaft was fabricated from 1/2" CPVC. 1/2" PVC could have been used but the smaller CPVC was used to keep mass down.
The figure below shows the plunger.
The catch engages the plunger through a section of brass tubing that passes vertically through the entire plunger shaft. The tube passes all the way through to give it rigidity and prevent twisting when the pistol is charged. Since the catch has to engage a single hole in the plunger, the orientation of the plunger had to remain the same for the catch to enter the hole in the plunger. To do this a indexing pin was installed through the receiver and into a slot cut in the plunger. The slot runs from the catch tube to about and inch from the end of the plunger shaft.
The plunger passes through a section of PVC that makes up the end of the pistol. The bearing section is made from a section of bored out 1/2" PVC and 1/3" coupler. The spring rest on this bearing section and presses on the plunger head. Because the plunger head is just glued on to the plunger shaft, a screw was placed through the plunger head into the shaft to insure the plunger will not fail. The Mk2 plunger head was redesigned to be more solid and the retaining screw was done away with. The figure below show the plunger assembly as it would come out of the pistol. The spring passes over the plunger shaft and the bearing section rides against the spring. The charging ring hooks into the back of the plunger shaft through two horizontal holes. When assembled the plunger assembly can be installed and pulled out of the pistol as a unit. The plunger is retained in the receiver with two pan head screws that are located on either side of the pistol and screw into the bearing section. The indexing screw for the plunger is installed through the top of the pistol and passes through the bearing section and engages the plunger slot.
Receiver
The receiver is simply a section of 1" thin walled PVC. The barrel and plunger reside in the receiver and are held in place with 1/2" pan head screws. The trigger mechanism is attached to the bottom of the receiver.
Frame
The frame consists of the section of the gun that is under the receiver that covers the fire control group, and the pistol grip. The horizontal portion of the frame is made from SCH40 1" PVC. It is beveled on its edges to fit nicely against the under side of the receiver. The pistol grip is made in the Boltsniper trademark way. The center section of the grip is 1" PVC. The forward and rear portions are half sections of 1" PVC. the pistol grip is bonded to the frame for rigidity. The trigger guard is cut from 1/1/4" PVC and sanded to the desired shape. A wire insert was pplaced in the trigger guard at the bend to add integrity. The guard is then bonded to the frame.
The prototype and the first Mk2 manufactured included accessory rails mounted on the underside of the frame. The rail is standard MIL-1913 and will take a variety of available accessories. The figure above shows the prototype frame with a tac light mounted.
Fire Control
As usual the trigger system was the last component to be thought fabricated and implemented. For this gun I stuck to a proven system. I basically used the same type of setup as you would find in any production Nerf gun. There is a catch that moves vertically and engages the plunger. A ramped section that travels along the axis of the gun wedges the catch away from the plunger and releases it. Taking advantage of the good ole simple machine...the wedge, to turn one motion 90 degrees. The image below shows the trigger system partially installed on the receiver. The aluminum plate transfers the motion applied at the trigger into a downward motion of the catch. The catch is made from music ware and is bent is a Z shape. This produces a horizontal section for the trigger plate to push on. A small piece of flashing fixed to the catch pin and a section of pen spring sits on that to apply a upward force to the catch for positive plunger engagement.
The trigger plate rides between two sections of PVC that have been ground flat. This constrains the motion of the trigger plate to purely linear and in the direction desired. A small hole is cut in the receiver just ahead of the catch. This hole is present to allow air in behind the plunger as it rushes forward during firing. If there were no hole a vacuum would be created when the plunger is released and it's speed would be greatly reduced.
The figure below shows the trigger plate uninstalled in the pistol.
The slot present in the middle of the plate is there for a retaining pin. A U shaped pin passes through the plate rails and the plate and prevents the trigger plate from moving away from the receiver. The U shape provides two pins that prevent the plate from rotating. The notch at the left hand side of the plate is the attachment point for the trigger spring. The trigger itself attaches to the plate at the top left corner and is fastened with a pin that passes through the hole in the plate.
All the components of the trigger system are shown below and are laid out more or less in the orientation as they would be installed on the pistol.
The pistol was constructed component by component starting with the internal components. the barrel and plunger were constructed first and the receiver was size around those components. The figure below shows the prototype about half way through construction. The plunger shaft is cut long and was shortened to the desired length later on. The pistol grip and fram have been cut but not bonded together yet. At this point there is no fire control components at all.
Further construction. the frame is fitted to the receiver and all screws have been set. The rear of the frame has been cut to retain the catch. The pistol grip has been bonded, filled, and sanded, but has not been attached to the frame yet. Pistol grip attachment was one of the last steps as the slot for the trigger must be cut in the frame and the grip.
the last major component to be fabricated is the fire control group. In the figure below the trigger system is competed and installed. The final cosmetic features like the trigger guard and iron sites are installed and the pistol grip is bonded to the frame.
The prototype was painted with a base coat of satin black Krylon Fusion. A matte black finish was then applied. the pistol grip is wrapped in electrical tape for grip and to prevent paint rub off.
After the completion of the prototype slight changes were made to the design. These changes included a CPVC barrel over crayola, modifications to the plunger head for reinforcement, and small changes in the manufacturing process. The new pistol was designated the Mk2 version of the BS-6 . Three Mk2's were slated to be built. One was completed and sold (SRL 102). Serials 103 and 104 were not completed and sat in storage. The uncompleted 103 was sold to a buyer that desired to complete the pistol. Serial 104 is still in storage and will one day be finished to be paired with the prototype.
Below is a figure of a Mk2 SRL 102
Detailed plans are available for download. They are presented in a spreadsheet with detailed drawings including dimensions.
GNS Plans <5.4 Mb>GNS Manual <1.0 Mb>
The plans were made with Microsoft Excel, a component of Microsoft Office, and are in *.xls format. I realize some of you may not have Excel at your disposal. For those of you who fall into this category, there is a free program suite available for download that will read *.xls files. The program is called OpenOffice and is available here.
Available for download are some videos showcasing specific points of the GNS.
Pistol Walkaround <2.52 Mb>
Shooting the Pistol 1 <2.0Mb>
Shooting the Pistol 2 <2.05 Mb>
Trigger Detail <3.14 Mb>
Trigger Mechanism <2.75 Mb>
First Person Action <1.55 Mb>
Take That <1.02 Mb>
And This <2.60 Mb>
And That <2.60 Mb>
EXTERNAL LINKS
All Image and Content © Evan Neblett 2006