Now that the barrel has been cross drilled and pinned place, it’s time to turn my attention to installing the rest of the barrel components. I’ll begin with rear sight block. This is pressed and pinned in place over the barrel and onto the top of the front trunnion. So… how do I arrive at the proper measurement for this ? Again — I cheat a little. I actually use the top dust cover of the receiver to determine how far down the barrel I press the rear sight block.
I’ll be pushing against the back of the receiver during this process. I don’t like to have steel on steel contact though. The ram do the press is hardened steel, and so is the receiver. So I cast a block of softer brass from empty rifle casings to push against the receiver. This way I don’t swage the rear trunnion and bend something important. It doesn’t leave any scratches in the finish either.
I simply press the receiver downward until the back lip of the dust cover fits into the slot at the back of the receiver. I go slowly to make sure I don’t press it too deep, and watch carefully in case there’s any flexing of the receiver walls. I know that a milled wall has more thickness than a sheet metal receiver wall, but I’m still watching for anything that looks like it’s flexing or bending. A generous amount of lubricant helps the parts slide together too.
Now it’s back to the knee mill to cross drill and pin the rear sight block into place.