NerfHaven: Shortened pumpsnap - NerfHaven

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Shortened pumpsnap

#1 User is offline   snakerbot 

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Posted 29 July 2011 - 03:36 PM

Alright, the story of this blaster goes back a few weeks. I've been following the homemade scene for a while and have really liked all the pump-action stuff, but was disappointed that they all seemed really long, especially once the barrel and hopper were added. So I set out with a goal: keeping the draw of 6” constant, and keeping a hopper, make a pump-action snap that was as short as possible. This is what I came up with.

Before I go into the writeup, I'd like to give credit to Daniel Beaver for some design aspects of the plunger rod, and to TantumBull for the ideas in his plunger-rod less snap.

Materials needed:
1 1/2” thinwall pvc
1 1/4” pvc
3/4” pvc
3/4” thinwall pvc
1/2” pvc
1/2” cpvc
1 1/4” pvc tee
3x 3/4” pvc endcap. At least one must have a rounded end
3/4” pvc coupler
3/4” to 1/2” pvc bushing
2x 1” to 1/2” pvc bushing
1/2” cpvc coupler
1/2” cpvc endcap
1/2” pvc wye or tee and coupler
1 or 2 clothespins
Roofing nail
L-bracket
12x 6-32 x 3/8” machine screws
8x 8-32 x 3/8” set screws
2x 6-32 x 1/2” machine scerws
1x 6-32 x 1 1/2” machine screw
1x 1/4-20 x 1 1/4” machine screw with nut
1x 1/4-20 x 2” machine screw with nut
A really short wood screw
2x 1 1/4” x 1/4” fender washers
1x 5/8” SAE washer
1x 1 1/4” rubber washer
1x 1 1/2” rubber washer
#10 finishing washer
1/4” ID nylon spacer
k26 spring
A small spring to use as a trigger spring
Your barrel of choice
and various tapes and adhesives

Whew! That's a bit. Note that this was everything I used to make mine. Your parts list may change slightly based on your choices.

Now. Before we begin, I want to show you a picture of the barrel I used.
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It's a 9/16” brass Brithop. (my darts are fat) The pvc part of it is 10 3/4” long. If you use a barrel that ends up with this part being longer or shorter, you will have to change some dimensions. I'll let you know which ones as we come to them.

Now let's start with the plunger head. This is a combination of the superlative and preeminent heads. The pvc ramp of the preeminent but the small size of the superlative. Drill a centered 1/4” hole in the cpvc endcap, then drill out a hole in the back of a 3/4” pvc endcap so that the cpvc one can fit through. If you have rounded and not-rounded pvc endcaps, you need a rounded one here.
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Cut down the pvc endcap so that it is flush with the end of the cpvc one, and fill the space between them with epoxy putty.
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Then sand it smooth.
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Glue one of the 1 1/4 x 1/4 fender washers onto this. Make sure the hole is lined up with the one you drilled. Then assemble the rest of the head as you would a superlative. I assembled it all quickly so that the first washer could be held in place while the glue cured.
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Cement your cpvc to the head. You need about 11” of it.
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Next you'll need to make a small ring of pvc and/or fittings. All that really matters is that the outside rides in 1 1/4” pvc and the inside fits over cpvc. I used 3/4” pvc endcap (actually the part cut off of the one on the head should work), 3/4” pvc, and and sanded down cpvc coupler.
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Now glue your 5/8” SAE washer to one side of it. The whole assembly should be 1/2” long. This piece is what the bolt in the priming slide pushes against to prime the blaster. The washer prevents the threads from digging into the pvc.
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Slide this piece onto your plunger rod 6 3/8” from the back of the head.
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Drill some 7/64 holes through it, and run your 6-32 x 1 1/2” screw all the way through, and your two 6-32 x 1/2” screws into the other sides. Cut off the heads flush with the edges of the pvc.
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Cut down the plunge rod so it ends 3” past the back of this piece you just put on. Then bevel the outside edge.
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You're done with the plunger rod. Onto the main body!

Cut a 30 5/8” piece of 1 1/4” pvc. If your barrel is longer or shorter than mine, you will need to change this dimension. If it's longer you could also just let the barrel stick out the front, but that would look like shit. You have a few slots to cut in the body now.

These are going to be some offset slots like on Daniel Beaver's pumpsnap. Drill 5/16” holes at 3 1/2” and 9 9/16” from the back of the body.
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Connect these with a dremel, scrollsaw, or whatever.
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To make the other slot, I inserted the plunger into the body, and put the drill bit through the slot I already cut, then around the plunger rod, and drilled through the other side. The end result is slots that will allow a bolt through without touching the plunger rod.
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Ending at 12 5/8” from the front of the body (meaning that you mark there and cut forward), make a slot a little bigger than your wye. I did this after making the offset slots so I could line this up where I wanted: A little offset to the right.
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Clean all the pvc shavings out of the body, and prepare to install the bushing. Instead of the normal 1” to 1/2” bushing wrapped in tape, I used a 3/4” endcap with a 3/4” to 1/2” bushing in it.
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This fit better in the body than the 1” bushing, and was slightly shorter as well. Cement them together.
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And cut the back of the endcap off flush with the back of the bushing.
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Don't slather the assembly in goop right away. Slide it in through the front of the body until it's sitting in the wye slot you cut out.
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Now you can cover it with your adhesive of choice. I used epoxy. Rotate it in the slot so you can get all around it. Then push it back until it's flush with the edge of the slot. Ignore the screws for a moment.
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Once the epoxy cures, drill 8 9/64” x 3/8” deep holes into the bushing, and insert your set screws into these holes.
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If (like me) your bushing lets air around between it and the 1 1/4” pvc body, you can dump hot glue into that nice little crevice made by the endcap and bushing to seal it.
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Time for the spring rest. Sand the ridge inside a 3/4” pvc coupler until pvc goes all the way through it.
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Cement this and an endcap onto some 3/4” thinwall pvc.
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Then cut the pvc flush with the coupler.
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Bevel the front edge.
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Wrap this in packing tape until it fits snug in the 1 1/4” pvc. Then insert it into the back of the body until only the rounded part sticks out. Use four 6-32 x 3/8 screws to hold it in. These will need to come out soon, but it's easier to put the threads in now. Sorry for not having a picture of the screws, but it shouldn't be hard to figure out. You can see them later as well.
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Part 2 coming in a moment.

This post has been edited by snakerbot: 29 July 2011 - 03:59 PM

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#2 User is offline   snakerbot 

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Posted 29 July 2011 - 03:48 PM

Up next is the pump slide. Cut the 1 1/2 thinwall to 20 1/2. Cut out a section 9 1/2 long, starting from one end. Make sure to leave more than a half pipe left, but don't leave a ton.
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Put your plunger in as far as it will go. It might help to put in your spring as well, as this will flatten out the rubber washers on the front. Before you can do that, cut your k26 to 10. (Cut off three coils.) When your plunger is in, line up the back edge of the priming slide with the back of the pvc ring on the plunger rod. Mark where the holes for the bolt need to be.
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Drill holes 5/8 from the back of the priming slide, big enough for your bolt to go through. In my case this was 1/4 for a 1/4-20 bolt. Go ahead and test how it fits together. Ignore the handle you can see below it. We'll cover that later.
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Remove the priming slide, and make a slot for the hopper to stick through. It should start at 9 1/4 from the back of the slide, and be 8 long. Where it goes radially will depend on where you put your hopper.
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Try to leave as much pvc in place where this slot is close to the other one. You can see I cut the corner at 45 degrees.

Set that aside(or leave it on the blaster, whatever) while we work on the trigger. Mark a spot 8 1/2 back from the back end of the slot you made for your wye. Drill the hole for your clothespin trigger's nail. This hole should be opposite the two slots you made earlier.
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If you want to, you can just use a normal clothespin trigger here, but my design places the catch face much closer to the rear of the blaster when it's primed. Because of this I wanted find a way to move the handle and trigger forward while still using the clothespin and nail combo for the catch. Here's how I did it.

Cut the nail and clothespin used for the catch like this, and glue it on as normal. This picture shows epoxy putty holding the nail in place. Don't do this, Use hot glue.
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Get another clothespin and take it apart. Cut half at the notch where the spring pushes on it, and cut the tail off the other half. Superglue the tails together like so.
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Affix your L-bracket to the piece like this. I used epoxy putty and a short wood screw. You will also notice that my bracket is too big and I had to cut it down. You'll probably be better off just using a smaller one.
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In the previous picture you may notice a slot in the wedge of the trigger. To make it, drill a bunch of holes slightly larger than the nail you are using for your catch. Then use a dremel or a file or just push the drill bit sideways through the wood until you have a nice slot. It should slide pretty freely around the catch nail. You can probably see where this is going.
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Pushing the trigger back will force the clothespin up, pulling the nail out enough to fire the blaster.

It's time for the handle. There are a lot of way to do handles. I made a boltsniper-style 3/4 pvc handle.
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With a slot cut out for the trigger mechanism.
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Attach the handle somehow. You can move it forward and back a bit so the trigger spacing fits your hand best. If you can find an adhesive that will hold the handle on by itself, congratulations. I couldn't, and after a few different tries, I ended up with something rather weird.
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Those are 6-32 x 3/8 screws in a slice of 1 1/2 thinwall pvc. I used the piece cut out of the pump slide. The heads of the screws fit into some slots cut in the handle. Epoxy putty then covers everything. This piece is glued onto the body, and then two more 6-32 x 3/8 screws are inserted through the 1 1/2 pvc into the body. These screws should line up with the bolt on the pump slide.

You can also see my trigger spring and some slivers of pvc I glued on to keep the trigger aligned. The spring behind the handle is only there because I fail at clothespin triggers. If you did yours properly you shouldn't need it. But just in case, here's a better picture of what I did.
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You're almost done! Just the barrel and stock left! For the stock, since there are some screw heads sticking out of the pvc, you will need to cut some slots in your 1 1/4 pvc tee to fit around them.
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If you haven't already, cut a short piece of 1/2 pvc, stick it into the back of the wye, and insert this in through the slot you made earlier. You probably won't be able to push it all the way into the bushing just yet. Make sure the plunger and pump grip are in place before you do this though.
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You should still have two 1 to 1/2 bushings left. Sand the ridge off one of them.
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Sand out the inside ridge from both, and wrap both in packing tape until they fit snug in 1 1/4 pvc.
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Stick the one without the ridge near the back of your barrel. Insert the barrel in through the front of the blaster, and push it into the wye. This is when you really push and get the wye to sit nicely against the bushing behind it. If you use a Brithop, make sure the halfpipe is lined up.
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You can also see in that picture the bushing in front of the wye.

Take the other bushing, and insert it in the front of the blaster. Using your last two 6-32 x 3/8 screws, screw it in place.
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Finally, it's done! Just stick on clear pvc and a dart door (or whatever) for your hopper clip.
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Have a firing video:


If you are wondering how much all that extra shortening work did, the whole blaster is 32 long.
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#3 User is offline   diamondbacknf1626 

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Posted 29 July 2011 - 04:37 PM

Hmm...cool. That sliding wedge trigger is interesting. I won't say anything about shorter being better for fear of the jokes that would ensue, but you get the point. However, there are a couple things that worry me. Most importantly, anything that's fastened with glue... No matter how secure you think that the trigger is, that the clothespin is, or that the roofing nail is, it's likely to let you down sometime. I'm not sure how you could work it out with your design, but mechanical fastening is always better. See here:
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That trigger will never fail, ever. Like I said, I'm not sure how you could work something out with your design, and I understand why you've chosen to go with it. However, this is something you may want to consider. This blaster is only 2" longer than yours:
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(With a barrel in the hopper that's the same length as yours)

Another quick note, but this is really just personal preference. You may benefit from developing some sort of sheath for your blaster that will cover up the priming slide as you prime the blaster so that it won't slice up your cheek as you prime.

Again, I like what you've done to improve the length issue with the initial design. I'm curious, what kind of draw are you getting? I may have missed it in the initial read-through...

This post has been edited by diamondbacknf1626: 29 July 2011 - 04:40 PM

QUOTE(TxNerfer @ Nov 13 2010, 12:42 PM) View Post

Hey...I got a crazy idea: how about you stop all that sigging stuff? It's not even my thread and it annoys me.
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#4 User is offline   aj1234119 

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Posted 29 July 2011 - 05:15 PM

I believe he said 6'' of draw.

I agree that this is a nice design, but the fault of this kind of pump action snap is that they will always be longer than the shortest slotted plunger rod pumpSNAPs with the same amount of draw, and the plunger rod will also be heavier, if only slightly. However, this is still a very nice blaster.
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#5 User is offline   snakerbot 

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Posted 29 July 2011 - 05:19 PM

I'm not super happy with all the glue either, but I tried to use mechanical fasteners whenever I could. The L-bracket for the trigger is actually screwed onto the clothespin. It's only the catch clothespin which is glued on. I didn't think it needed a screw since there isn't a lot of force on that part, it's all held by the nail up front. Now that I look at it though, there is room for a screw there as well. I'll have to do that on my next blaster. I also have an idea on how to build the handle differently that would prevent the epoxy putty mess there.

As for the sheath, I thought about that after i finished this. >_< It isn't a big issue for me though. I'm right-handed but left-eye dominant, so I don't shoulder the blaster to the point where it would be a problem.

I don't know exactly how much draw this one has. The plans I have on paper say it should end up at 6", but I think this actually has slightly more.

aj: Really? I couldn't see how a slotted plunger pumpsnap would be shorter. Maybe without the barrel, but mine puts the priming grip up there.

This post has been edited by snakerbot: 29 July 2011 - 05:24 PM

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#6 User is offline   aj1234119 

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Posted 29 July 2011 - 05:39 PM

Well the plunger rod must be the length of the spring and the distance between the catch and the plunger head on a snap like the one you've built, while with a slotted plunger rod it just has to be the length of the spring, so if you built the blaster so the plunger rod touched the back of tee when primed, your style would have to be slightly longer.
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#7 User is offline   snakerbot 

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Posted 29 July 2011 - 06:02 PM

Ah. I see what you're saying now, but you're actually mistaken. The catch is in the plunger head like a normal snap. What I believe you are referring to as the catch I call the spring bushing. It's there to keep the plunger rod centered, to provide something for the bolt in the priming slide to push against, it's also the piece the spring pushes on to move the plunger. And the plunger rod isn't the distance between those two plus the length of the spring. It ends only three inches after the spring bushing.
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So when it's fully primed, the 3" of cpvc after the spring bushing end up inside the spring rest. The compressed spring is around that cpvc, with the 3/4" thinwall pvc around that.
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#8 User is offline   aj1234119 

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Posted 29 July 2011 - 06:06 PM

Oh, sorry my fault for not reading the writeup thoroughly, i actually read that after i replied.
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#9 User is offline   durka durka 

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Posted 29 July 2011 - 06:12 PM

I know this might seem like a stupid question, but the k26 spring can be found on mcmaster, correct? I'm planning on doing something like this and I don't want to order the wrong part.
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#10 User is offline   snakerbot 

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Posted 29 July 2011 - 07:43 PM

View Postdurka durka, on 29 July 2011 - 06:12 PM, said:

I know this might seem like a stupid question, but the k26 spring can be found on mcmaster, correct? I'm planning on doing something like this and I don't want to order the wrong part.


Yep! McMaster part number 9637K26.
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#11 User is offline   MrPzowned 

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Posted 30 July 2011 - 05:29 AM

Here's a good idea for when attaching the stock. On the back where there had to slots cut, I would've cut the slots in an "L" shape and and rotated where I cut the slots on the stock so that when I had to put on the stock it would be at an angle, and then you could twist it over into place. Kinda like taking the barrel attachment off of a LS or any N-Strike blaster that has an additional barrel, except, this would be taking off the stock. This would allow easier maintainence acces to the back of the blaster.

This post has been edited by MrPzowned: 30 July 2011 - 05:31 AM

17:54 Noodle Yes what he did was stupid
17:54 Noodle but it's a plastic toy
17:54 Gears BUT IT COULD'VE BEEN MY PLASTIC TOY
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#12 User is offline   Blue 

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Posted 30 July 2011 - 07:42 PM

I enjoyed reading your write-up. Thank you for the short blocks of text and informative pictures (and also for a firing video that is actually a firing video instead of boring talk about how cool your gun is) ; also cool that this looks like it can be replicated with normal tools and local hardware parts. Keep up the good work!
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#13 User is offline   Daniel Beaver 

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Posted 01 August 2011 - 07:37 PM

That's using your noggin - placing the pump grip over the barrel section is a very clever design decision. And it ends up being a whole ten inches shorter than my SNAP! But the again, I do have a soft spot in my heart for absurdly long blasters...

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#14 User is offline   windtex1 

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Posted 11 August 2011 - 05:08 AM

A couple of things: First off, I like the plunger head design, I use(d) something very similar to that in the snaps I make. Second, the lever trigger is... interesting, is there any reason you decided to go with it? What are the pros/cons? And lastly, instead of having to cut all those slots in the tee for the stock, you could have gotten a slightly longer screw and screwed the stock in. Or, you could use the same screw and drill a hole in the tee (well, 4 holes) the size of the screw head. Then insert tee, and put screws in. Lastly, I don't understand why people use a "sheath" for their hopper clips, it just adds more weight, even though it looks badass...Overall, nice design.
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#15 User is offline   snakerbot 

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Posted 11 August 2011 - 02:46 PM

Pzowned:
Interesting idea, but really not necessary. The tee stays on just fine as it is, but can still be pulled off if I need to get in to the plunger.

windtex:
It's less of a lever and more of a wedge. The primary reason for this was so the handle doesn't have to be behind the catch. If it was, then either the stock would be too short for my arms, or I would have to make the whole gun longer to make the stock comfortable. A side benefit is that the trigger slides straight back, which I prefer to pivoting triggers. The main con I see with it is complexity. It's certainly harder to make than a normal clothespin trigger.

As for screwing in the tee, I considered that, but it would be hard to hold the spring rest in while the tee is in place, since there is a little pre-load on the spring.

By "'sheath' for their hopper clips" I assume you're talking about the 1 1/4" pvc extending all the way to the front of the blaster. That's simply because the pump grip needs to be up there. Watch the video again and look where I put my front hand.
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