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Blaster Design and Instructions by Ryan McNumbers

Forum Threads:

July 2010 - 06:40 PM

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My main reason for doing this project was to take advantage of hopper clips, and them being so awesome. Having a pump action blaster, as opposed to having a normal pull back style blaster, increases rate of fire tremendously. It's also very beneficial to your accuracy. Instead of taking your hand off the main handle, pulling back the plunger, and putting it back on the handle, you have one fluid motion without changing your stance, or aim.

So, here is the Pumpbow.

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Of course mad props to Captain Slug for the Plusbow, and Split for that marvelous skirt plunger head.

The basic power system, catch and trigger are all very similar to the +bow. I added a few things I thought would make the original design better, aside from making it pump-action.

First thing to do was improve the handle.

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I removed the trigger guard and replaced the two piece of polycarbonate on the grip with a solid piece of wood. The worst part of the +bow is the handle, specifically where you put your middle finger. This, for me, is much more comfortable. I used small rubberbands (for braces) for the trigger return. I also beefed up the catch spring to give the trigger a harder pull. I did this to prevent accidental fire, in absence of the trigger guard. Before my war this weekend, I'll also wrap the handle in some foam for extra comfort.

Next I needed something to link the foregrip to the plunger rod.

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I used a 1/2" x 1/2" square aluminum bar for the plunger. The priming bars are 1/4" x 1/2" aluminum bars. To link them, I just used a 1/4-20 steel threaded rod, 2 1/2" inches long. That random shit in the back of the plunger is actually some hot glue wedged in there because of a miscalculation while using the mill. Whoops. I can work on something more permanent later, but it works for now. Also, it's pretty much imposssible to use any other tool other than a mill for the channel in the plunger rod. It's unfortunate.

Here's a better view, while it's being primed.

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And what it looks when it looks like when fully primed.

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Next order of business is the priming handle, or foregrip.

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It's mainly composed of two 1 1/2" x 5/8" 90° angles. Those are screwed into the aluminum priming bars, and to a 1/8" piece of polycarbonate on the bottom. The foregrip assemblage is guided by two 1/8" UHMW polyethylene bars that run the length of the draw, keeping the foregrip from moving down. The 90° angles ride 1/16" underneath the bottom plates and prevents the grip from moving up. The polyethylene works well since it has relatively low friction. The aluminum on aluminum rubbing isn't ideal, but it's not going to mess up the blaster at all. Next one I make, I will probably improve upon that. The grip is actually surprisingly comfortable. I enjoy this a lot more than a large semi-circle. I've sanded down the edges, and will probably put some type of foam on this later. Another thing on my to-do list is get a rubberband or extension spring moving the foregrip forward after being priming. 

Last thing I did was make the stock shorter.

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The whole blaster is roughly 4-5" shorter than a traditional plusbow. It actually fits in boxes! With the stock being about 3" shorter, I can get a lot more leverage on the foregrip, making it much easier to prime.


Miscellaneous stuff:

I used a K25 instead of the K26 (+bow), to make it easier to prime. It gets 6.5" inches of draw. With Slug darts I'm getting plusbow ranges, with almost three times the rate of fire.

Here's the firing video.

Overall, I'm extremely happy with this blaster. I can, and probably will provide some general templates/parts list for the design if anyone wants to attempt to build one. I might do a writeup in the future as well.