IF you want to be nit picky specific - get an SA in the 3 Mil or below. The HRA was only made durring the Korean War.
I have seen Very Few problems with the standard BFAs available. I think the expensive one talked about here is the one with the locking colar & BFA made in one piece. A Hollywood type BFA is one that is inserted(screwed) into the bore so it doesn't show.
Sarge