I made a quick barrel to first test how well a standard 12" PETG barrel did. I decided to use my Pump Shotgun as the gun to test the barrels, mainly because it's one of the only couplered guns I have.
So, for the tests, I pushed a dart into the back of my heavy wall 12" PETG barrel, then pushed it up a bit so it was at the position it would be if I had loaded it with a breech, to keep things constant.
I shot it 3 times, using the same dart, and pushing it up roughly the same distance.
The dart landed an average of about 100' (From where I shoot, there's a wall of bricks almost exactly 100' ahead of me, and it either hit the bricks, or dropped right at them).
I then used the same barrel to cut my breech. So I started by marking then cutting the hole for my breech.
Sorry these pictures have horrible white balance, it was dark outside, so I had to use the work light in my room.
The cut is roughly 1.75" long.
Then I needed to make my breech cover. I cut a ~2.25" section of medium wall PETG for this. I then cut this piece lengthwise using a pair of scissors.
Then I slid it over the heavy wall PETG barrel. I sealed off one end, then blew down the other to see how good of a seal this basic set up had. It was terrible, air leaked out all over the place. So to improve this, I wrapped the breech cover in e-tape.
And here it is, breech closed.
I tested this set up to see if the seal improved, using the same procedure as before. It worked. The seal was so much better. To keep this seal, the slit I cut, now a small gap, had to be on the opposite side of the cut breech. To make sure this side was always down, I drew a line over it with a sharpie so I could tell where it was.
And the whole barrel, breech installed.
I had to spray silicone lube over the parts that the breech cover contacted since it was really hard to move back and forth.
I went outside and range tested again, using the same dart. I shot it 3 times again, and to my surprise, the dart went the same distance as before. I don't know it was because of the breech, but two out of the three shots, the barrel blew off. I think it was because I put the barrel in the coupler looser so I could pull it off without risk of it breaking.
Now, there are some definite downsides to this compared to a brass breech:
-The whole thing is flimsy, the section of the barrel that was cut for the breech can twist from side to side and it feels very weak. I don't think this will matter too much though, as it should normally be encased in PVC.
-The breech cover is harder to move back and forth, even with the silicone lube.
-Occasionally the breech cover will catch on part of the breech hole when it's closing. This really only happened when I was trying to close it really fast, but fast is how it will always be closed in a war situation.
-The added e-tape will make it tougher to add a breech handle.
I think I can work out some of these flaws. This was only a quick prototype. I'll update this as I solve these problems, or if I come across anything else worth noting.
Hopefully I can get this whole thing to work well. Maybe in the future perfectly nesting materials won't be necessary for a breech.
Edited by Retiate, 21 April 2008 - 04:56 PM.