This blaster is a refinement of a refinement of a refinement of a refinement. At it's core, it is a derivative of Carbon's SNAP 7.5 Pump Crossbow, which is itself a refinement of his SNAP 2. I took the idea and ran with it. What sets the SNAP 7.5 style blasters apart from Stark's style (of which Nerfomania's design is a derivative) is that the priming action is in front of the catch, rather than behind. Though behind-catch-priming-blasters are much shorter, they are more complicated to build, requiring a lot of dremel cuts. The design I'm presenting in this writeup is very simple to build, requires no specialized parts, and delivers absolutely top-tier performance.
A couple of things to note before you start building one:
- This blaster is very long - the main body is 32", and the total length is 50" if you add a hopper and 16" barrel. If you are very short you will have trouble operating this blaster.
- This blaster has 6.5" of draw. This is detrimental to the long-term health of the spring, so you'll need to replace it every so often.
FYI, you can click on any of these pictures to get a full-sized view.
* Optional materials
- Power drill
- Drill bits to go with it (1/16", 1/4", 1/2", etc)
- * Tapping bits
- Rotary tool (dremel)
- Reinforced cutting disk
- Sanding bit
- * Diamond cutting wheel (better for cutting plastics)
- Pipe cutter
- * Three-sided drafter's ruler
- 1/2" cpvc
- 3x 1/2" cpvc couplers
- 2x 1-1/4" OD 5/8" ID SAE washers
- epoxy putty
- PVC cement OR superglue
- k26 spring
Plunger head <- don't feel obligated to follow this exact design
- 1-1/2" OD 1/4" ID (or smaller) rubber washer
- 1-1/4" OD 1/4" ID (or smaller) rubber washer
- 5/6" OD 1/4" ID (or smaller) rubber washer
- 1/4" bolt, 5/8" long
- 1/2" CPVC cap
- Silicone grease
Plunger tube and stock
- 1-1/4" sch40 PVC
- 2x 1-1/4" coupler
- 1/2" to 1-1/4" bushing
- 1-1/4" elbow
- 3/4" PVC endcap
- 3x 6-32 screw, 1/2" long (5/8" and 3/4" also works)
- Heavy-duty clothespin
- 1-3/4" roofing nail
- Metal L bracket
- Epoxy putty
- Hot glue
- 2x 1-1/2" PVC coupler
- 1/4" bolt, 5/8" long < DO NOT USE BRASS OR ALUMINUM
- Tape or glue
- Donation blaster
- 1-1/2" PVC
- 1/4" set screws,
- 4x 6-32 screws, 1/2" long (3/8" or 1/4" are be better, but sort of difficult to find)
- Epoxy putty
- Hot glue
Here's an overview of the internals.
The key design feature of this blaster is the way the priming bolt works. Here's how it looks from the outside.
The bolt in the priming handle sticks into the slot, and catches on the front washer, allowing you to push back the entire mechanism. The clothespin trigger then catches on the rear washer. You may ask: why do it this way? After all, in my previous writeup, the priming bolt just pushed directly against the catch face, instead of this extra washer. There are several reasons I think this system is superior:
1) You don't have to cut a slot into the priming grip. This slot was doubly annoying because it neccessitated a 3rd 1-1/2" coupler to be added to the grip in order to give you enough space for your hand.
2) It gives you enough clearance to use a zip-tie to hold the clothespin in place. Mechanical fastening is far superior to adhesives.
We're going to start with the plunger rod, since it's dimensions dictate the geometry of the blaster.
The catch faces are built from 5/8" SAE washers sandwiched between 1/2" couplers. Fit them together, and then use super glue or PVC cement to securely fasten them. There should be no "give" at all. Once you've glued them, build up your ramp using epoxy putty. You can also use a PVC ramp if you prefer.
SAE washers are sometimes difficult to find, so there's an alternate way to do this. Use endcaps insead, and dril and tap 1/4" holes in them. You can then use any old 1-1/4" washer.
Might have to widen the washer hole first.
For a plunger head, I use a sandwhich of rubber washers, with a 1-1/4" metal washer to act as support. A 1-1/2" rubber washer acts as the main seal, and a 1-1/4" rubber washer sits behind that to prevent it from shearing against the metal support washer. In front of the 1-1/2" rubber washer, I use a small 5/8" washer, and I bind everything together using a 1/4" bolt. Most people use a second metal washer on the front, but I don't - I think the diameter of the bolt head is plenty wide. All this screws directly into a CPVC cap, and I usually add goop for support and seal. I use a 1/4" tap on the CPVC, and no nut. But if you don't have a tap, you can just drill a 1/4" hole through the CPVC cap, and then secure it using a nut. If you DO use a nut, consider flipping the direction of the bolt, so that the nut faces outward. This will let you adjust the tightness easily once the blaster is assembled. I couldn't find 1-1/4" metal washers with a 1/4" ID, so I just put them in a vice and drilled out the center. EZ PZ. Properly lubricated, this plunger head will give you a 100% seal.
There are lots of ways to build plunger heads, so don't feel obligated to use this design. Build whatever you're familiar with.
Next up is the spring rest. Use a 3/4" endcap, and drill out a 5/8" hole. That's problematically large, but there are serveral ways to do it. Most people just drill a 1/2" hole, and then widen it with a dremel. I acutally use a 5/8" drill bit, but it's too large to use in my drill. So I... improvise.
Let's get the measurements right before we glue anything together. The distance between the priming face and the plunger head coupler should be 7.5". All the shell cuts are going to depend on that presumption, and also the presumption that we are using a 1/4" bolt for priming (you can't ignore the width of the bold when making measurements!).
I'm also assuming the distance between the front of the plunger head (remember, the washer flares forward in the tube) and the rear of the plunger head coupler is 1.5". If your plunger head is significantly shorter or longer, it might screw up some of the dimensions. I have very loose tolerances built into all of these measurements, so it probably won't be an issue.
Let's take a look at the plunger tube. I highly suggest using a three-sided ruler for these, since you can lay it flat against the curve of the tube and make very straight lines. First, draw a centerline all the way down the side of the tube.
Next, mark the spot where the spot where the back of the coupler meets the plunger tube. For my design, I'm using a bushing and an external coupler, so that spot is just the very end of the plunger tube. But...
...if you use an internal coupler, such as with rork's SNAPbow mk5, that spot will be an 1.25" or so into the plunger tube. Set the coupler next to the plunger tube, and mark the plunger tube where the back edge of the coupler lies. All futher measurments are based on this mark, so get it right!
First, mark a spot 8" away from your front point. Then make another mark at 7.75". Make a third mark between those two - this is where you will drill with a 1/4" bit, to make the front of the slot. We're going through this rigamarol to ensure that the 1/4" bolt fits, and is properly positioned.
Next, we mark the rearmost point of the priming slot. It will be 7" away from the rearmost front slot mark. Make a second mark at the 6.75" mark, and then a third inbetween those. Finally, use your ruler to connect the outer edges of the hole marks to act as a guide for our dremel.
Next we mark the hole for the trigger. Grab your plunger rod, and place it up against the rearmost mark on the slots, and make a mark in front of the catchface.
The actually trigger hole is going to be on the opposite side. You COULD put it on this side, if you wanted. I initially wanted to do that, but the bolt head presses against your palm in that configuration.
In order to mark the other side accurately, I made a little guide tool. I cut off an edge of a 1-1/4" coupler, and then made marks on all the compass points. This slips snuggly onto the plunger tube, and allows me to accurately mark the opposite edge.
Slip the spring onto the plugner rod, and stick the spring rest on the back. Place the front of the plunger head at the "front mark" (where the coupler meets the plunger head), and then make a mark behind the spring rest. This will be one of the spring rest holes. Use the guide tool to make a mark on the opposite side as well.
We're done measuring, time to cut.
Use one of the roofing nails to make marks where you're going to dril. Start with a 1/16" drill bit, and work your way up. For the slots, make 1/4" holes as the end, and then use a dremel to cut the slots. When your finished, run a 1/4" along the slot to make sure there are no tight areas. I recommend a diamond cutting wheel for this job, as it works a lot better than other cutting wheels.
Next is the priming handle. Simply glue together two 1-1/2" PVC couplers, and then stick a 1/4" wide 5/8" long bolt. You can't use any other length - 3/4" is too long, 1/2" is too short. Drill the hole fairly close to the edge, and then tap it. Try it with the slot to make sure it slides freely. You don't need to glue the couplers if you don't want - wrapping some gorilla tape around it works just as well. If you have access to 1-1/2" thinwall, you can use a short section of it between the couplers.
You need to use a steel bolt here - aluminum or brass will begin bending in no time. You also need to use 1/4" or larger - don't skimp on this part.
Make a trigger and attach it. If you are unsure of how to do this, check out the SNAPbow mk5 writeup - my triggers are identical to his. SNAP triggers are, of course, a total bitch to get working correctly, but are very reliable once you do. There's no need to use anything more extravagant than hot glue. The zip-ties do most of the work.
One thing I do differently is that I drill a double-long hole for the nail, and then set it against the rear of the hole. The clothespin ends up supporting all of the force of the plunger, but the priming action and trigger pull is much smoother as a result. Carbon has gone into great detail as to why this is a stupid way of doing it, but I think he's full of shit. Who ya gonna believe, Carbon or Me?
(Be sure to drill it a little more straight than I did in this picture. I also drilled this hole on the wrong side of the blaster. Durrr)
For the handle, I used a donor nitefinder handle. After cutting it off, fill the open end with epoxy putty (being sure to wedge it into little nooks and crannies). Once that has set, attach a piece of 1-1/2" PVC is using 1/4" set screws. I fill the sides with hot glue to provide lateral support. The 1-1/2" PVC clips onto the main body of the blaster, and the screws hold it in place. This type of handles is comfortable, and rock-solid. It is also easily removable, so you can use your use your favorite handle on your next blaster.
Ultimately, handles are a very personal thing, and you should use whatever style you are most comfortable with.
The last bit to make is the stock. I used an elbow and a coupler, stuck a short section of 1-1/4" PVC between them, and then glued them together. The stock is secured to the blaster via a single screw on the bottom.
Time to assemble everything. Lubricate the plunger head with silicone grease - accept no substitute. Run the plunger head through the blaster a few times to get it lubed up, adding a little bit each time. Add a hopper and barrel - 16" of CPVC is what I would recommend.
Done. With the hopper it clocks in at 230 fps on my chrono, about on par with +bows.