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Detachable Breech

I'm looking at you, crossbow and maxshot users.

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#1 ompa

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Posted 15 April 2015 - 03:19 PM

So for those of you who remember me, I (still) hate clips with a passion. This design COULD be adapted to accept a clip (increase the size of the breech, move the "bolt" handle L-shaped cut ahead, create a clip well, and expose more of the larger of the two nesting brass sizes), but I think I'd rather run through a swarm of bees than deal with modified darts/clips again. Anyways, this clip does a decent job of minimizing dead space, can be put on (nearly) any springer, and still allows one to swap to the multitude of barrels that some of the old Crossbow users used to carry around to maximize fire rate.

Here is a picture of the completed breech attached to my scuffed-up and poorly-painted maxshot (a product of my poor choice in paint. Kids, don't buy crappy paint.)

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Materials list:
-small and preferably strong magnet (bet you didn't see that one coming)
-length of 1" cpvc
-length of 1/2" pvc
-2 different diameters of brass (I used 9/16 and 17/32, the key is that they are able to nest)
-hot glue
-JB weld or another very strong epoxy
-"Bolt" handle (use whatever you want; if you've got a plastic rod that would probably work better for the purpose of bonding, but I used a brass piece)
-random scavenged objects that are preferably metal and somewhat L-shaped (I cut up some hanging picture wall mounts I had sitting around).

Tools:
-Dremel
-Hacksaw
-Pipe cutter
-Hot glue gun
-Ruler (or calipers, finger(s), lengths of string)
-Tape?

***As usual, my guide will eschew any highly specific measurements, due to differences in darts, and preferred barrel lengths***

First, you're going to want to take your length of 1" cpvc. The minimal length requires this:
-length of pvc that will sit in coupler at base (a centimeter or two)
-length of the L-cut (determined by length of dart + 2x the width of your "bolt" handle)
-Length after the L-cut to allow for the inner barrel to be stable when moving, which will likely consist of the width of the collar used to allow the inner barrel to sit straight (but not snug) in the 1" cpvc, plus the travel distance of the barrel (this is to make sure that when the collar moves, it still remains inside of the 1" cpvc). In the picture, the collar I'm talking about is the black tape, but I replace this with something else later.

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Measure and map out where you're going to want your "bolt" handle to be, and make sure it's long enough to be as long as the dart is + 2x the width of your "bolt" handle. Also while you're at it cut the breech opening. Next, take a piece of your 1/2" pvc, and take a cm or so (not so long that it appears when looking perpendicular to the breech. This is so that when the actual breech is closed, there is at least a little overlap of the nesting brass to create a solid seal) and glue it in the back. This little piece can actually end up being a somewhat high-stress area after repeated usage, so don't just jam it in there with some tape.

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Next, take your 1/2" pvc, and drill a hole the width of your bolt handle at the base. The distance between the base of the barrel and the hole should be approximately equivalent to the small space you left above, between the 1/2" pvc stub and the actual start of the breech hole in the 1" cpvc. The whole reason for this hole (heh) is to give the bolt handle a little more support. I know a lot of breeches in the past have been plagued with problems of trying to attach two pieces of pipe at 90 degrees, and it causes some issues. This helps alleviate the stress a bit. Your larger nested brass barrel will go in here. I strongly suggest you glue it in here, but only after the hole is drilled; otherwise you risk hitting the brass, denting it, and ruining the whole project. I had my brass nearly flush, but it's ultimately up to you. You're going to want only the brass exposed if you want to take this further and do a clip mod, but for this project I do not do that.

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Next, you're going to want to take your smaller nested brass length, and cut your actual breech. I used a bit of tape and glue to bridge and center the brass inside the 1/2" pvc stub, and you can see the black tape on the right side of the picture. I also sanded and polished all the edges to minimize friction between this piece of brass and the other piece of brass that will be sliding over it.

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Next, you're going to want to put everything together. This part I'm sure is fairly self-explanatory; the smaller nested brass (with tape or whatever bridging material you used) is attached to the 1/2" pvc stub, and the barrel goes in the other side. This is where the collar comes in to play. I used some packing tape due to the slick surface, but Ideally you would use a bench grinder/lathe/even a belt sander to sand down a 1/2 coupler, and use that as a collar. Even more ideal would be just to prototype a part. Unfortunately, I have none of those things so I'm using packing tape. Next, put the bolt handle in. Make sure the joining surfaces are clean and rough, and use the JB weld to make that joint secure. I then took the two L-shaped metal pieces I had listed in the materials list and used them here. One of them is bonded at the junction of the "bolt" handle and 1/2" pvc junction for added support. The tiny magnet I used is also bonded to this spot. The other L-shaped piece is bonded to the 1" pvc. This serves as the point where the magnet attaches when the breech is fully open, preventing it from flopping around if you're moving. I know there's a spring in the picture, but after a bit of trial and error I don't think it's really needed if the magnet is being used. A spring strong enough to open the bolt by itself I feel just adds unnecessary stress on the bolt handle. Also I apologize for what looks like a somewhat sloppy JB-welt job, I haven't gotten around to cleaning up the appearance yet.

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Anyways, at this point you should be all done. Here are pictures of the breech open and closed:

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Unfortunately I don't have any range values or chrono numbers, although I hope to pick up a chronograph sometime before the year is over. Or maybe next year. It's a long-term goal really, since I'm never going to find an area I can safely shoot it in and measure the values any time in the near future. No it is not war tested, or stress-tested yet. I will of course revise the guide if I run into problems in the future, or ideas for improvement, but for now it stands as-is. It's certainly not a perfect breech setup, but it gets the job done.

~ompa
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#2 OzNerf-Sarge

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Posted 15 April 2015 - 07:46 PM

Have you seen Nerfomania's CPVC/PVC breech guide? It's a little simpler to make and can be done with 1/2" and 5/8" PETG barrels as well.
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#3 ompa

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Posted 15 April 2015 - 08:00 PM

Actually, I had not; that's pretty brilliant. Unfortunately, for the darts I use, cpvc is a bit too tight to use in that style of breech, and I don't exactly have easy access to PETG. But I gotta admit, that method is far simpler and superior for those who have access to the materials. Thanks for pointing it out!

~ompa
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#4 OzNerf-Sarge

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Posted 15 April 2015 - 08:07 PM

The main benefit of brass over PVC is the tolerances are a LOT tighter than PVC; I have yet to find 17/32" brass that does NOT sheath with 9/16" seamlessly. PVC and other plastic pipes can often be too loose or too tight within each other; the two different pieces of 20mm conduit I use in Titanturion (one for the barrel guide and one for the breech) are a perfect example of that: the 16mm conduit is too tight inside the barrel guide and loose within the breech. This, incidentally, happens to be ideal, but that's a different point altogether.
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#5 ompa

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Posted 15 April 2015 - 08:20 PM

That's generally the reason I've stuck with brass. It's a pain in the ass to work with, it's a hell of a lot more expensive than pvc, but once it's done I don't have to be too worried about issues cropping up later. Also, having moved several times, the only consistent material I seem to be able to get a hold of is this god forsaken expensive brass. The only 1/2 PVC they carry at my local home depot doesn't actually nest with the cpvc at all; I just checked because I was interested in the far simpler breech video you posted. Even stranger is that it is not the same size as typical SCH80 or SCH40 pvc (ID too large for SCH80 but too small for SCH40), and it didn't even have a label on it. Apparently though it's the only 1/2 pvc they sell though.

~ompa
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#6 OzNerf-Sarge

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Posted 15 April 2015 - 08:23 PM

That's generally the reason I've stuck with brass. It's a pain in the ass to work with, it's a hell of a lot more expensive than pvc, but once it's done I don't have to be too worried about issues cropping up later. Also, having moved several times, the only consistent material I seem to be able to get a hold of is this god forsaken expensive brass. The only 1/2 PVC they carry at my local home depot doesn't actually nest with the cpvc at all; I just checked because I was interested in the far simpler breech video you posted. Even stranger is that it is not the same size as typical SCH80 or SCH40 pvc (ID too large for SCH80 but too small for SCH40), and it didn't even have a label on it. Apparently though it's the only 1/2 pvc they sell though.

~ompa


Having worked with both PVC And brass, I love brass that much more than PVC anyway. Wait until you see the next blaster write up I have templated (I only need to add my pics for it onto Photobucket and I can finish it); it's so brass involved you may have a Nerfgasm.
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