Is it an H&K or Italian SBE? That will give you a place to start. If the older version, number 1, get a replacement ejector as they tend to wear out and break, especially with heavier loads. Second, if its the older version, go with something in the .665 to .675 range, newer .655 to .670. Coincidentally, my old H&K and my SBE II both like the pure gold .670 and straight hevi 7s and mag blends.