I am not a machinist, so how do you get the 90 degree inside corners in the receiver for the breach block? Broach?
There are many ways to do that, broaching, filing in using "file fixtures" similar to methods used in the 1800's by gun makers*, casting and wire cutting/EDM.
This projects receiver started life as a Rodney casting then I have modified it. Also to insure the mortise was true I did take a skim cut using a Wire EDM. So you can see many ways to skin the kitty. On the floor plate which has a much more complicated mortised thru slot I have milled and filed it to shape and will also use broaching to complete the final work required on it.
* a task generally reserved for the apprentices as it was hard physical work.
