Neanderpundit

This is where the complexity of the geometry starts to bite

If you aren’t cutting a square, which almost nobody does, then you have to make sure the part you’re cutting is capable of being cut. This shape, no matter how simple, cannot be cut.

You cannot cut a sharp inside corner using a round tool, The only thing you can cut is a round inside corner, and cut the sharp corner, if it is necessary, in a separate operation.

Look at the slide opening in my PPX.

There are NO sharp inside corners. Even the breechface has rounded corners, the barrel has simply been designed to mate with that. This means that no consecutive operations are required to make it square. That means when you put this chunk of metal into a machine, it comes out complete, and is ready for finishing and assembly. The 1911 slide, by comparison, needs about 30 operations after it is initially machined.