SNAP-1 MK2
NAVIGATION
The SNAP was initially created for me to experiment with what I was learning from Boltsniper's guns, without having to attempt building an entire FAR. The SNAP-1 came about as a way to use my plunger design and trigger mechanism, but ended up working well enough that it stands on its own. My initial goal for the SNAP series was to incrementally recreate the functionality of a FAR. However, these guns seem to serve a purpose all their own, as easy to build spring-based blasters with great range. They're just simple, highly effective guns that you can build in an evening.
The mk2 designation is due to the number of improvements since the gun was designed: namely, a stronger trigger, and a number of plunger improvements (better seal, and weight reductions).The SNAP-1 operates like most any Nerf spring-based blaster. The plunger is primed by pulling a rod in the rear, and loaded via the breech (or muzzle loaded, in the case of fixed barrels).
All materials for the SNAP-1 can be found at most any hardware store.
Pressure Chamber:
1.25” Sched. 40 PVC
1.25” PVC Endcap
1.25” PVC coupling
1.25” x .5” PVC reducing bushing
Plunger:
.75” thinwall PVC (Sched 40 will work)
.75” PVC Endcaps (x2)
Cotter pins (I used 3/32”)
.5” aluminum rod (wooden dowel will work)
3/16” x 1.5” rubber fender washer
#6 Finishing Washer
5/32 x 7/8 washer
#6 x .75” Oval Head machine screw & nut
9.5” x .5” spring (you can find this at True Value or Ace. It fits around a .5" rod.)
Handle:
Split key ring
Trigger:
Clothespin (plastic is best)
Small nail (not finishing, needs a wide head)
Small angle iron
Small zip ties
Barrel:
Barrel material (crayola, brass, etc.)
.5” Sched 40 PVC
Tools (bare essentials):
Hacksaw
Power drill and bits
Sandpaper
Hot glue gun
Not essential, but will make things easier:
Pipe cutter
Small files
Dremel
X-acto knife
The SNAP breaks it down to the three essentials: a plunger, a barrel, and a fire control system.
Plunger/Pressure Chamber
The plunger of the SNAP is constructed of a short section of .75" thinwall PVC and two .75" endcaps riding in 1.25" sched 40 PVC.
The gasket assembly is composed of a finishing washer, a neoprene fender washer, and a metal fender washer, all bolted to the front endcap. The rubber fender washer is larger in diameter than the ID of the 1.25" PVC; this increases the seal. The finishing washer bites into the rubber washer, causing it to cup upwards. This makes the rubber washer hug the walls of the PC.
The charging end of the plunger goes through a simple 1.25" endcap. Holes are drilled to relieve pressure during cocking and firing.
The charging rod is attached to the plunger by means of a cotter
pin. The rear endcap is rounded to allow the nail firing pin to
slide up and over, to lock in place in front of the endcap. After time,
this part can wear. However, I've never had a failure yet, and the
endcap is replaceable in the event of failure.
Trigger
The trigger mechanism, like the rest of the gun, is meant to be simple. The firing pin is a nail which extends into the pressure chamber. When the plunger is pulled back, the rear endcap slides over the nail, pushing it down. The nail then clicks back up when the endcap passes. This holds the plunger in place until the trigger pull.
The basis of the trigger is a standard spring clothespin. A hole is drilled through the jaws, and a wide-headed nail is used as the firing pin. The nail is roughly trimmed to length, filed smooth, and the head glued to the clothespin. Fine adjustments to the firing action can be made by shimming the clothespin jaws.
Further experiments with the firing pin have shown that a 1" roofing nail is very effective; it is stout enough so it won't bend in an accident, and wide enough that the pin can be filed off at an angle to assist in the endcap sliding over the top. The head is also wider, so it can be placed on top of the trigger mechanism, strengthening the whole trigger.
The physical trigger is a piece of angle iron, although anything suitable can be used. This is what I use, as it's easily found, standard, and cheap. The trigger is glued to the clothespin ,and ziptied in place for security. It would also be possible to simply epoxy the trigger in place for a more permanent solution.
The trigger is covered with a piece of PVC for aesthetic reasons, as well as helping to keep the pin from pulling completely out of the hole.
Barrel
The SNAP guns are built with a modular barrel system. It is able to use
stock micros (PVC/crayola), micro stefans (17/32" brass in .5" PVC),
and mega stefans (21/32" brass in .5" PVC), all quickly
interchangeable. All fixed barrel bases are .5" PVC stubs, with brass
fitted inside.
The end of the pressure chamber is fitted with a 1.25" PVC coupling and a 1.25" to .5" reducing bushing. Barrels simply press into place, and can be replaced quickly and easily. Barrels of different sizes could be carried in a war to allow for usage of any ammo found on the field, be it micro or mega stefans, or even stock darts.
17/32" & 21/32" brass, breech barrel, hopper clip & Crayola PVC
A hole is drilled through both the PVC and the brass, and cotter pinned. The hole is then sealed with glue.
The barrel that the SNAP is shown with in this writeup is the pump action breech, which is the subject of another writeup. The breech is .5" PVC, with 19/32" brass by the breech area. That brass is fitted to 17/32" brass. The 19/32" brass seats against a rubber washer, which in turn presses the dart into the 17/32" barrel section by about 1".
The trickiest aspect of construction is determining
where to place the trigger. To do so, you need to measure the draw of
your plunger. Use a pushrod and measure how deep your PC is at full
spring compression. Mark that spot. Then, remove the plunger. Lay the
marked stick next to the PC, and your plunger at the end of that. This
way, you can visually determine where the catchface will fall. Mark a
spot about a half inch forward of there; you need to be able to pull
the catchface past the firing pin, and let it come forward to lock in
place.
It's also not essential to round the end of the catchface plunger, if
you don't own a dremel tool. The only drawback is that in order to
prime the gun, the trigger would have to be held down. It's possible to
round the endcap with files and sandpaper; it would just take a
long time.
The rear endcap can be screwed to the plunger body with no concern.
However, the front coupler also should be screwed down. If your screws
are too long, they will protrude into the plunger tube and destroy the
gasket. One option is to make sure that you buy short enough screws.
Barring that, you can predrill holes, and then trim your screws to
length with a hacksaw or dremel.
There are no set lengths for this gun; it's mostly determined by what
you can find as far as a spring. The spring will determine your draw,
which will determine trigger placement. The length of your spring will
also determine the overall length of your gun. The basis of the SNAP is
experimentation...take it to the tube, see what works, and try it out.
See the links and downloads section for full construction guides and photos.
Full construction guide <420 kb>
Assembly guide: http://nerfhaven.com/forums/index.php?showtopic=6232
Breech assembly guide: http://nerfhaven.com/forums/index.php?showtopic=6280
All Image and Content © <Mark Wooldrage> 2006