If the gun was converted to straight grip as you say was it also lengthened? If it was who knows what material was used. The welding could have had an annealing effect on the parent material. Does the guard show any case colors? I don't know that any of this matters except to explain why the material is so soft. It won't matter in the tang area of the guard when it is screwed into the wood. I can't imagine that heat treating will effect the strength of the guard around the trigger itself. So unless you are restoring the case colors I don't think I would worry about it.
Bill G.
