Smyth Busters: Can You Mix & Match Bolt-Carrier Groups?

Brownells, Inc.
Brownells, Inc.
175,263
0
Published 2022-09-20
One of the great things about the AR-15 platform is its interchangeability of parts. This includes the ease of swapping a different bolt-carrier group into your rifle, which takes all of about 20 seconds. But some folks out on the Internet say, "Don't mix and match AR-15 bolt-carrier groups!" Why not? Let's ask Steve and Caleb.... who say AR-15s are all manufactured to the same specs, so a new bolt-carrier is almost certain to fit in your rifle. Just whip out the headspace gauges and check the headspace on the new BCG. You don't even need a full set of headspace gauges. Just a NO-GO gauge is fine. (Don't use a "field" gauge: that's for military and law enforcement users who put a very large number of rounds through their rifles during training.)

Here's another warning about mixing and matching bolt-carrier groups: Let's say you have two BCGs that both headspace correctly in your rifle. You set one of them aside and shoot thousands of rounds with the other. Don't just swap the "spare" BCG into the gun without checking the headspace again. The lug recesses in the barrel extension have worn while you were shooting with the other BCG, and the spare bolt-carrier group may no longer headspace correctly. How many rounds lead to significant wear? That varies by rifle, type of ammo, gas system pressure, and a lot of other factors. Suffice it to say, the average casual shooter is probably not going to significantly wear the headspace on their rifle any time soon.

So the myth is BUSTED, with a stipulation. You CAN change your AR-15's bolt-carrier group IF you check the headspace when you do it.
All Comments (21)
  • @CalebSavant
    Just because you can say "I did it and nothing bad happened" doesn't mean you should keep doing it. We all know this guy right? Oh, and I said I would timestamp it! 4:27, Steve said check it!
  • @douglass69
    You need to show the gauges and explain exactly what you’re talking about for us that don’t know.
  • @britjohnson1990
    Its still incredible to me that almost any new bolt and any new barrel will headspace just fine.I dont know anyone who really have had any headspacing problems with any half decent company's products. Its no wonder why its such a popular design. You could never do that with any design that locks up in the receiver. Modern machining and tooling is incredible. I dont see this platform being replaced for 50 years
  • @jerroldkazynski5480
    The Army had a series of cartoon-ish publications giving hands-on experience tech talks for the care and feeding of M-16s. Wish I had kept them.
  • @chad9166
    We need a set of mugs with Steve and Caleb's likenesses on them
  • @2ndchance632
    Interesting. I’ve been ruining two different BCG’s in my AR-15 for years. One is from Aero Precision and the other is from BCM. Checked both with go/no go gauges. Never had an issue with either one. Round count in thousands for both. As always, keep the myth busters coming. I really enjoy watching them. 👍🏻👍🏻
  • @KendrasEdge757
    I think the main issues occur when you’ve used a well used barrel and swap the BCG with a different well used BCG. Typically if you put a new bolt in on a used barrel you’ll be ok because the average person will never shoot out an AR barrel or BCG.
  • @danielczech30
    Many years ago, I was qualifying on the range with an M16A2. I had 2 lugs sheer off of my bolt. I had the range armorer grab the bolt from the weapon of a Marine being dropped from the range at the same time. I ran it without issue.
  • @OmegaBahn
    I love the interaction! Headspace gaging is so useful even if you think you're rifle you won't change astronomically between uses.
  • @cheatingdeathcustoms2244
    Always good to check. It doesn't take a lot of time and it can save you a lot of headaches. Great video.
  • @Zestypanda
    Love the educational, entertaining videos you make. Also like that you do make videos on our questions.
  • @kenneththiessen1674
    I really appreciate your discussions on these gun smithing topics. Thank you for all the good info.
  • @sxsboy2253
    Thank you for this one ! I have built 5 uppers, including threading the barrel and setting up the barrel extension AND getting the gas port solidly in between the rifling lands. Each one has its own bolt (BCG) mainly because I don’t trust manufacturer’s acceptable tolerances. A lot of guys I shoot against that are truly competitive and do the same thing. Some of the guys at the range say other wise and think it’s waisted money to have so many bolts, but I also never see those guys at the prize table either. Truth be told I’m not at the prize table much anymore either but that’s because of the ol’eyes.
  • @GunWillTravel
    This is exactly why Mil Spec matters! Drop in a new BCG, and it just runs. I've never had a headspace issue, actually. But tuning the weight of the BCG and buffer with the spring and gas system definitely can affect operation.
  • @Rcasca1
    Hey guy's, I learned something here today. Thank You. I was under the impression that a new AR-15 build did not need to be head spaced. Thank you for the honest information.
  • @joshuabruce9920
    I'm only like 2.5 years into being a gun enthusiasts so I don't really have an opinion yet I'm still forming one. I learn something new almost everyday, I really do love YouTube as a resource for learning
  • @davidforce5617
    I was an armorer MOS 2111 for 10 years in the Marines and I have literally inspected thousands of M16 rifles including a 3 year tour at MCRD PISC and the amount of rifles that failed headspace could be counted on one hand with fingers left over. I dont remember replacing any BCGs but we did replace plenty of the gas carrier keys.
  • @SavageTactical
    It’s definitely prudent to check the headspace on used ARs and when you swap out barrels/bolts. I have seen barrels that would not pass a go gauge and have had one where the receiver extension not aligned properly.
  • @Quality_Guru
    Here is a video worth watching after this myth buster - "Brownells Tech Tip: AR-15 Headspace". Thanks for the intel.
  • @twssr1955
    Another informative video. Headspace is very important. Thanks for the information and recommendations.