12L14 isn't very strong even though it's steel. If the screws are
holding
the gun together and are under load and or shock you should be using
a
medium carbon steel and heat treating.

I've used 1144 for such purposes. Where 12L14 is a little weak,
the 1144 machines almost as nicely and has less cold-shortness. 110ksi
is about right for strength, IIRC. No heat treatment required.

Dan