Swarfmonger is correct, the bottom of the breech casing sides are on centerline, or the top of the frame rails, right side drawing correct.
I didn\'t radius the brass side rails, but I did make a fixture to hold the side rails in position while brazing. I had used high temp silver alloy, actually silver brazing, my breech casing was made from thicker material, so I bored it and left it a little undersize, then silver brazed the sides on and the oscillator track on the bottom, the casing gets distorted with the high heat, then honed the ID of the breech casing to final size. I think a person could get by with using silver bearing solder for this instead of silver brazing, I think 4%Ag / Sn solder has a liquid temp around 450°F. This is what I used for soldering the oscillator assembly and my drum magazine. I think I would have used it on the breech casing too.
I had silver brazed the magazine base assembly 48-23, but would have used silver bearing solder there too if I ever make another one.
I am not sure what others have used on the breech casing, whether they \"silver brazed\" or used \"silver bearing solder\".