I have a bolt carrier group left over from an upper I sold several years ago. The guy I sold it to didn't want the BCG and it's been sitting in a box in a closet since. I'm getting back into ARs and want to order a new upper. Is there any reason I shouldn't just re-use the BCG from the old upper with the new one? I'd rather avoid buying a whole new BCG if possible. They are the same brand (BCM) and I only put about 200 rounds through the old upper with the BCG.