Respectfully

A hardness test will not be enough information to determine the yield point of that barrel. One would need also to know its chemical composition.

Further there are a number of steels that if incorrectly heat treated will give appropriate RC values but are subject to embrittlement if not heated or cooled correctly through certain critical points. 4140 for example is one of these.

If that information cannot be determined then it is far better to throw it in the scrap bin at this point.

Regards.