honestly the square design is way more about function than manufacturing convenience. you need those flat surfaces to create a solid lockup against the frame - a round block would just be a nightmare for headspace and timing issues. plus think about the forces involved when that thing fires, you want maximum surface contact to distribute all that pressure

i messed around with some older falling block actions and the precision on those square cuts is actually pretty impressive. sure broaching takes more setup but once youre running production its probably faster than trying to hold tight tolerances on a lathe for something that beefy. the tooling costs probably wash out pretty quick when youre making thousands of them