A-36 is the equivelent to cold rolled steel. It's fine for allot of things but not gun parts. If the part has allot of wear potential, like a hammer and sear, then it needs to be made out of tool steel and hardened. If it's a frame or slide it doesn't need heat treating but the material needs to be tough, like 4140, 4130, or some stainless. These have a fairly high rockwell number so they come fairly hard.
Speaking of hardness a file is about 65-70 rockwell. Hard but brittle. The hammer or sear are usually about 54-60 rockwell and that material could be A-2, D-2 or some of the less common tool steels. The frame and slide would be about 28-32 Rockwell and could be made from 4140 HT, it's pre hardended but can be machined with high speed cutters but it tends to work harden when machined so you might eat up allot of cutters. Carbide is best and indexable carbide with flood coolant is even better.