Repro frame alloy?

[Chuck Heald]

Originally Posted by Linn Matthews

Edgar
Thanks for your note. Would you please comment re your thoughts of what treatments would produce the best receiver?
Thank you

Linn

In modern guns, the receivers are often made of 4140 hardened and tempered to mid 30's Rockwell C scale.

The RBL is an example of a 4140 frame. On my visit to the CSM plant, Tony told me that they pre-hardened/tempered the frame blanks prior to machining. This did two things for them.

First it reduced the grain size of the steel and allowed for finer finish of the machined surfaces. Normalized 4140 machines poorly and leaves a rough finish. Slightly hardened, it machines with fine finish, albeit it takes a bit more energy to cut.

When a part will never be welded, 4130 and 4140 can have a small amount of lead added as an alloy to facilitate better machinability. This addition doesn't affect mechanical properties much from a practical standpoint. However, the RBL has a welded on upper tang.


Second, it eliminated distortion from heat treat after machining.

[Autumn Daze]

I believe the same holds true for 200 series Stainless Steel. I remember machining 203EZ Stainless and it left great finishes. There are also some leaded low carbon steels that machine great but I can't remember the series. Chuck you might be right about 4140 for the Repros. But it does machine lousy.