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Pump Action Breech

An addition to other's work

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#1 Carbon

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Posted 26 March 2006 - 08:57 AM

I've posted the breech that I've made before, as a part of the clip on the SNAP-2. I was never that wild about the clip, but the breech always had a nice, solid feel to it (it was based off of ompa and Renegade's breech). So, I decided to put a proper style of pump handgrip on it.

This is the breech as it was before.
Posted Image

And the underside. The only difference from what I did before is that the 9/16" brass by the breech is a lot longer before it hits the 17/32" brass, about 2" (the length of my darts). It works well pump style, but the problem was how to attach something to that pipe clamp. The clamp and the endcap were key.
Posted Image

One inch thinwall to the rescue. I cut a rectangle in some PVC with would allow the clamp to sit inside it. The other part of the equation that I don't show here is the .25" section of endcap that I cut off to act as a guide. That section sits on the breech between the breech opening and the pipe clamp opening, and I installed it after putting on the thinwall.
Posted Image

One the hole was in place, I used two lengths of heavy ziptie going across the hole to press against the pipe clamp and keep it solid. I glued it in place.
Posted Image

Here's how the breech looks when open.
Posted Image

And closed. I made the 1" long enough so that it comes up to the end of the SNAP-1 PC. If I wanted to be cosmetic about it, I suppose I could drill a pattern of holes in the breech shroud and make it look like a Sterling. I could add the clip back on by cutting a hole in the shroud so it can pass by a clip. But for right now, it's a lot of fun to play with.

Edited by Carbon, 21 February 2008 - 10:02 PM.

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#2 GeneralPrimevil

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Posted 26 March 2006 - 09:06 AM

Nice adaptation of the brass Unknown breach. I think this deserves to be put with the Unknown Breach writeup on this site. That's all up to cx though...

I think I'm gonna figure out how to do that with PVC Unknown breach. That way I can use it on my guns, especially the SNAP knock-offs. Which reminds me, going to Lowes today, should be picking up the fittings and whatnots that I need to complete those. Then I just will take a Jeep up there and pick up the 10' lengths of PVC I need.
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#3 Team Slaya

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Posted 26 March 2006 - 11:12 AM

You. Are. My. HERO! This is exactly what I need for a possible homemade I'm working on. I don't really see how the clamp fits in the PVC though. A bit more in-depth writeup would help me out a bunch.

TS
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#4 murakumo32

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Posted 26 March 2006 - 01:56 PM

Hmm. I have an idea, but I can't explain right now. Thanks Carbon!

I have a question about your dremeling, how do you get perfect rectangles like that? I just bought a demel myself and I've been practicing, but I have a hard time making semi-perfect shapes and such. Can I get a tip or two?
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#5 Carbon

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Posted 26 March 2006 - 01:59 PM

I don't really see how the clamp fits in the PVC though. A bit more in-depth writeup would help me out a bunch.

Well, for the initial breech, I had the long slot cut out where the clamp slides back and forth. What I did was take a small clamp and place it in the slot. I then slid the brass up and through the PVC, and through the clamp. I then tightened down the clamp to make it solid.

As far as how the clamp fits in the shroud PVC, the screw on the clamp sticks a little past what the ID of 1" thinwall is. Cutting a hole at the spot where the clamp sits allows it to stick out and have the shroud push against it. The additional piece if .5" endcap (which isn't shown) keeps the 1" centered...otherwise, it would only be sliding on the whole endcap. I used small pieces of ziptie in teh hole to give additional surface for the screw to push against, and just glued it in place.

I'll try and do a writeup when I get some more brass.

As far as Dremeling, I use a few tools to get my finished results. I'll start the ends of the rectangle with a hacksaw, and then do the long straight lines with a dremel. Once I have the long shape roughed out, I'll do some more work with an X-acto knife, and then finish up the edge with sandpaper.

Edited by Carbon, 26 March 2006 - 02:03 PM.

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#6 Jangadance

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Posted 26 March 2006 - 04:36 PM

Very good breech, I'm especially excited about attaching the pipe clamp to the brass, I couldn't think of a way to do that properly before seeing this pictorial.
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#7 Carbon

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Posted 26 March 2006 - 06:05 PM

Range testing!

It was a beautiful day today...sunny, 40 degrees, light breeze, so I got some testing in with the breech, attached to the SNAP-1:

Into the wind, 14 shots, hip height, high (97') and low (71.5') tossed out:

Low: 71.5
High: 88'
Avg: 78'

With the wind, 9 shots, high (121') and low (80') tossed out:

Low: 84'
High: 105'
Avg: 94'

My building has odd winds around it, so I did some tests on the opposite side. Besides, the sidewalk there has blocks that are 5' long...easy to measure. 9 shots, (lost one), high (128') and low (80') tossed out:


Low: 80.5'
High: 121'
Avg: 94'

For yucks, I did a measurement with a fixed 17/32" brass barrel. Low (69') and high (93.5') tossed out.

Low: 74'
High: 92'
Avg: 82'

Edited by Carbon, 26 March 2006 - 06:07 PM.

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#8 fobpawwor

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Posted 26 March 2006 - 10:10 PM

Wow, that looks very helpful for a fast action rifle. Plus love the idea of using a pipe clamp. Amazing!
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#9 ompa

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Posted 26 March 2006 - 10:24 PM

Very nice, very nice indeed. Clean and well-executed.

However, do you have any ideas how to get the pump to go back and then forwards instead of forwards and then back? because then it would be really easy to integrate your breech with your SNAP to allow for a one-motion priming action.

~ompa
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#10 Carbon

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Posted 26 March 2006 - 10:33 PM

However, do you have any ideas how to get the pump to go back and then forwards instead of forwards and then back? because then it would be really easy to integrate your breech with your SNAP to allow for a one-motion priming action.

The best idea I've had so far is to work with the backwards motion of the bolt, but convert it into forward motion using a dual rack-and-pinion gear system (two racks, one pinion). Pull the one rack backwards, turning the pinion, causing the other rack to move forwards. The motion is exactly what I need to integrate the two systems, but I'm not sure where to find usable parts yet. Not that I've really looked at all, but still.
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#11 ompa

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Posted 26 March 2006 - 10:35 PM

You have to keep that backwards motion. At all costs.

I'm guestimating that I'm at least losing 15 feet of range due to the kind of bolt system I have in place on the SOFAR and (will loose) on the NEAR. The extra space just does not help things. I'd switch to using the other bolt system I used, but then I'd need a pulley system like you described, and that would just be a huge pain in the ass to make.

~ompa
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