What's the main difference and does it really matter which one you put in an AR? A guy I know said he thinks full auto bcg's run better. From what I've read, full auto's are a little heavier and may help with chambering and accuracy?
from physical inspection, i can tell you an AR-15 BCG has more relief cut into it at the back of the bolt, on the bottom. so, physically yes is more stout. if that means anything in real world applications i dont know.
I had a Bushmaster with a semi-auto BCG and now have a Noveske with a full-auto BCG. But the guns are set up so differently that it would be tough to make a direct comparison.
If the prices are the same might as well go with the FA BCG. You never know when you'll want to run your upper on your buddy's M16.