Moving BCG to new upper

AR/M4 AR Technical Discussion
1

I know that swapping BCGs between two uppers multiple times is not good. But what about permanently moving a slightly used BCG into a new upper? I have 200 rounds through my current upper. The BCG has a few wear spots already, but nothing serious. Would it be a bad idea to move into a new upper?

2

Not really. But, I still think it would be a good idea to do a headspace check. Having said that if the parts are of good quality, it would probably not be an issue.

3

Why is it possibly bad to move a BCG from one upper to another?

4

I’ve always heard it was more of an issue with the bolt itself due to lug wear than the carrier.

5

Primarily due to the mention in the Technical Manual which talks about swapping bolts, which is a headspace issue.

6

So you’re saying that the repeated firing of the BCG/upper combo somehow wears them in together in such a way that they become “married”? They have comperable wear characteristics that are unique to that combo, and moving the BCG to a different upper will make them “mismatched”?

7

That’s always been my understanding. I don’t think it’s so much a safety issue as it is a reliability issue. IE the bolt is essentially lapping itself into the receiver extension. If you put a worn bolt in a different barrel (receiver extention) you could have headspace issues.

8

I think you mean the barrel extension. :wink:

9

Yeah, barrel extension, you got me:D

10

So how does this all work with the MRP system? One BCG and different barrels?

11

Quote:
Originally Posted by Iraqgunz
Primarily due to the mention in the Technical Manual which talks about swapping bolts, which is a headspace issue.

So you’re saying that the repeated firing of the BCG/upper combo somehow wears them in together in such a way that they become “married”? They have comperable wear characteristics that are unique to that combo, and moving the BCG to a different upper will make them “mismatched”?

If I understand, the situation might be a BCG/Upper that has not had the headspace checked, not so much them not being mated/married. I don’t think that there would be a problem swapping if you verified that all components were safe together. Someone please correct me if I’m mistaken.

Keith