OK, STEEL M39-2 explained

[gmborkovic]

Hello Mr. stans, my metallurgy class was back in 1969. I remember that stainless steel came in a lot of configurations. I believe Series 316 was the least magnetic. I dont know what series BII or S&W use in their guns.
Hey, it was 55 years ago, and it was the '60s.

 

[stansdds]

I think 416 is the most commonly used stainless alloy for firearms.