Updated: 2/1/2006

INTRODUCTION

BS-3 and it's resulting failure ended by Homemade career in Blacksburg.  I graduated in May of 2003 and went on the job hunt reducing homemade time to nil.  In January of 04 I started grad school at VCU and found a temporary apartment.  the homemade bug bit again and I decided to attempt a pistol.  I wanted to build a scale pistol.  A 1:1 scale homemade pistol to any common auto pistol.  I got my dimensions and started designing.  the pistol was going to be short at about  7 inches long.  The barrel was to fit a standard sized dart so the barrel length was fixed at 3" the rest of the gun would be devoted to the plunger.  As I was in a temporary apartment I had limited resources available for materials and construction.  The resulting pistol is very basic, with many flaws and shotty construction.  The pistol was worked into a functioning prototype but resulting performance was so bad that it was not further developed into a practical weapon.

SPECIFICATIONS

Description...........Scale Cocking Pistol

Designation...........................BS-4

Release Date....................March 2004

Caliber.........Nerf Micros, Micro Stefans

Operation..............Single Shot Cocking

Propulsion.................Elastic Plunger

Magazine..............................None

Mag Capacity...........................N/A

Overall Length........................7 in

Barrel Length.........................3 in

Max Rate of Fire....................15 RPM

Max Range............................25 ft

Effective Range......................15 ft

Accurate Range.......................10 ft

Intended Use..........None cause it sucked

DESIGN

Length constraints due to the 1:1 scale criteria reeked havoc on the design of this pistol.  The barrel length was set at 3" to accommodate a standard dart.  This left 4" for plunger and propulsion.  A spring would take up a substantial amount of room so I decided to incorporate elastic bands that were housed above the receiver.  This would allow the plunger to be retracted to the very rear of the receiver giving it the most travel possible.  In addition to that I did not have any springs that I would have worked well at the time and I was feeling too cheap to buy anything. 

The issue encountered while attempting to use  bands was there had to be some connection between the plunger and the rubber bands above the receiver.  A operating rod had to extend out of the plunger.  This meant a slot had to be cut in the receiver.  The slot would allow all the air out from in front of the plunger and leave nothing to propel the dart. 

The solution was to move the operating rod to the back of the plunger and have a long section that would be sealed in the receiver.  The resulting layout is shown in the schematic above.  This idea could have been extended further and a much long plunger could have been used for a longer compression stroke.  But I didn`t want anything to protrude from the gun even when cocked.  Remember this was supposed to be as scale as possible.  The resulting plunger stroke was about 1.5".  the above drawing is not quite to scale. 

Following the scale them, I wanted to have a scale operating trigger.  A catch was fabricated out of a piece of plastic and protruded into the receiver to engage the plunger.  The catch took the shape of an L to form a bell crank that could be pushed by a shaft from the trigger.  A paper clip was used to transfer the motion of the trigger to the catch,  A section of elastic band was bonded over the catch to give it a positive engagement force.  There were no pivot connections between the transfer rod and the trigger or catch, so the system only worked in compression.  there were dimples in the back of the trigger and catch that the transfer rod nested in.  Not the best system but it worked temporarily. 

Standard 1/4" rubber bands were used for power.  They were hooked on the operating rod of the plunger and fixed at the front of the receiver.  Bands could be added to vary the power of the pistol.  With 8 bands on the gun it would fire about 20 feet.  Adding more bands could bump that up to 30 but they usually snapped off the bases when fired. 

I was thoroughly disgusted with the performance of the pistol.  There was no real room for major improvement besides a complete redesign.  I did learn a lot from the working on this pistol.  Everything I learned to do and not do was manifested in my 6th homemade the GNS.  If the pistol had performed better I was going to incorporate a slide on top of the receiver that would cock the plunger and return forward.  Again with the scaleness.  And of course it was to get a paintjob.  This project was effectively canceled when bad performance along with a move out of my apartment occurred. 

Ordinary PVC  piping is the main material used in the construction of the SCP.  The sizes used are as follows:

• 1" 200 psi PVC    (Receiver, Slide)

• 1/2" PVC Couplers    (Barrel spacers, Plunger)

• 1/2" PVC    (Barrel)

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. 

There are a very few number of components in this pistol.  Basically there is a barrel, plunger, receiver, and pistol grip.  Minimalistic.  

The red piece of plastic protruding from the piston is the operating rod that attaches to the rubber bands.  It passes through a slot in the receiver.  On the underside of the plunger is a notch cut for the catch engagement.  it is not visible in the above figure. 

The operating rod of the plunger extends above the receiver and the elastic bands are attached from the receiver hard mount to the operating rod.  The catch is attached to the receiver through mounting studs bonded to the power side of the receiver.  The pistol grip attaches to the receiver and covers the catch. 

The trigger pushes a rod that pushes on the catch at the vertical end of the L.  This action transfers the horizontal motion into vertical motion and pulls the catch tang down.  The image below shows the trigger system as it is installed on the pistol.  The pistol grip covers the catch.  A piece of wire is used to connect the trigger to the catch.  Holes in the pistol grip allow the rod to move and keep the motion constrained.  The wire is not connected to the trigger nor the catch.  Eventually, I was going to improve the trigger system and connect the transfer rod to the catch and trigger.  Dimples in the back of the trigger and the catch kept the rod in place when the trigger was depressed.