You're doing the exact same thing I did on my first Angel Breech Recon attempt. You've got the half pipe backwards. It goes on the barrel side. The half-pipe slides inbetween 1/2" and 19/32" brass on the slide and it stays between them.
My second attempt isn't finished yet, but I can get you dimensions for everything except the length of the 19/32" because mine is different.
Barrel Side:
9" total,
6" of 9/16"
3" of half-pipe
Slide
4.5" of 1/2"
1" 17/32" and 9/16" stablizers. This isn't definite, they just need to be long enough to center the 1/2" and short enough not to touch the back of the barrel when the breech is closed.
As for the 19/32", it needs to be long enough both to completely cover the 1/2" and to engage the catch. I used to have the measurement, but I changed my design a while back and lost it. Sorry!
Thats actually not mine, it was lifted from someone elses mod. I havent begun constructing mine. However I am seriously considering tossing it all out the window and using cpvc, because it slides into the clip just as nicely as 19/32.
I am not keeping the catch or any other internals aside from the clip lock and the trigger, because I am putting and AT2k inside of it. I wanted a clipped 2k so I am using the recon as a base. So far its going decently and I just need to know how the two pieces connect.
There does seem to be a problem with the math on the breech here, and it's one I've been working on myself as well. It doesn't matter if you look at Fallen Angels
original write up or Hereticorps' excellent
End to End guide they both make mention of using a piece of 9/16" for the half pipe. The issue I found with this is that the opening on the Recon/Longshot magazine is only 7/16" wide, so the half pipe would never fit inside it (the magazine).
After messing with it at length and almost ruining my Recon, I realized what an idiot I was being and how the half pipe works.
You load the magazine withe the breech closed. This allows the length of 19/32" to guide the side walls of the magazine around the breech entirely and thus delivering the half pipe inside of the magazine.
Then again, I could be wrong about this but if so, please someone say so as this is the only way I see the whole thing working out.
"Budo is a lot like life. You make mistakes. You learn. You sweat. You cry. You grow. By training in budo, you will come to be able to solve any of life's dilemmas. The answer will just be there." ~ Dr. Masaaki Hatsumi