Wow, Never heard this one before...

[RallySoob]

I call a local gun shop inquiring about Bolt Carrier Groups as I need one for my AR15. He tells me he does not sell BCG's because they would have to be properly headspaced for a specific upper/bbl to work right. He said "They aren't lego's, you cant just swap BCG's with different uppers and go...they will blow up the cases that way"

I always thought headspacing was regarding the bbl and bbl chamber, not so much the BCG. Am I missing something or is this GunSmith/Local Shop Owner gone crazy?

Is he right? I can't use just any BCG with my AR? Because I have used 2 different BCG's in this gun so far and never had an issue...

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[wichaka]

If its not matched to the chamber, I would have it head spaced.

 

[Lange22250]

In theory you don't need to do anything. In practice it's nice to check with a set of go/no go gauges.
I have never had a problem with any ar's I've built.
Having said that, as the bolt and barrel extension wear they may become some what "mated" to each other. I would not mix used parts together if I had the option. If I remember correctly the barrel and the bolt should have a similar life span. Replace one, replace both.

 

[RallySoob]

thanks for the info. Instead of getting a gun show bcg I went to Ole's Gun Shop here in Salem and found they have a guy that knows more about AR15's than most. He's a competitor/builder with some very impressive AR's... He said in theory you should be able to buy any new bcg and drop it in but it doesn't work like that because so many different mfgs are making these guns that it's impossible every mfg to make every part to the same spec in perfection. The difference between no go and go is like 3 hundredths or thousandths of an inch or something. Bottom line is, you can't change the head spacing on a bolt, you can only swap out different bolts until you find one that fits your bbl chamber. He used the go, no go gauges. I ended up getting a new RRA BCG complete and head spaced correctly for $135. Oles is by far the best gun shop in Salem. I've been to them all... It really is. These guys are genuinely nice, not a bunch of ‘hard *** know-it-alls' like most. They earned my business for a lifetime