AR15 headspace

[CodyK]

I’ve put together several AR lowers, but usually buy complete uppers. This time, I ordered the barrel and other parts separately. Should I worry about the bolt I have headspacing correctly with the barrel extension on the barrel I ordered? Should I get some go/no go gauges, or is “mil-spec” “mil-spec”?


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[Txhillbilly]

I value my firearm's and body parts too much. I check / set the headspace on every barrel that I install on any rifle.

 

[Mike_from_Texas]

I don’t and I’ve built several in various calibers.

How would you plan to fix it if there was a problem?


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[TexMex247]

I've put together a dozen over the years and the only hiccup I had was from a bolt that didn't always go into battery. I swapped that out with a quality carpenter bolt into the same carrier and the gun ran fine. It was a budget gun I built with a KM tactical bcg. So you get what you pay for. With quality parts you won't have any problems.

 

[Big Green]

I’ve put together several AR lowers, but usually buy complete uppers. This time, I ordered the barrel and other parts separately. Should I worry about the bolt I have headspacing correctly with the barrel extension on the barrel I ordered? Should I get some go/no go gauges, or is “mil-spec” “mil-spec”?


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Essentially not a big deal as long as you buy from reputable folks. I’ve built MANY, and never had a problem.

I believe @zackmars usually gives the best answer though.

 

[Bozz10mm]

Just for your peace of mind it wouldn't hurt to purchase a no go gauge. Or take it to a gun shop and have them head space it. I have purchased several uppers and lowers separately and some complete rifles. Not that it makes a difference.The only one that failed a no go gauge test was a complete AR from Bushmaster. It was fine with a field gauge. Even tho they offered to RMA it, I opted to try a new bolt and that fixed it.

 

[Mike_from_Texas]

Just for your peace of mind it wouldn't hurt to purchase a no go gauge. Or take it to a gun shop and have them head space it. I have purchased several uppers and lowers separately and some complete rifles. Not that it makes a difference.The only one that failed a no go gauge test was a complete AR from Bushmaster. It was fine with a field gauge. Even tho they offered to RMA it, I opted to try a new bolt and that fixed it.

How do you headspace an AR with a fixed barrel extension?


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[zackmars]

Essentially not a big deal as long as you buy from reputable folks. I’ve built MANY, and never had a problem.

I believe @zackmars usually gives the best answer though.

I appreciate the vote of confidence lol.

If you buy quality parts, you'll be fine, however if you're slumming it with BCA or radical, or are dealing with heavily used parts, then you may want to use some extra caution.

I've built a lot of uppers, over 30 if i had to guess, and headspace has never been an issue. But the "lowest end" barrels I've used were from faxon and BA.

My taste now is pretty vanilla, I'm not saving any money by building, vs buying a complete URG.

 

[Bozz10mm]

How do you headspace an AR with a fixed barrel extension?


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[CyberWolf]

It's still worth checking, IMHO, because you can run into an issue with tolerance stacking - even with parts from quality manufacturers (I have). If so, swapping parts around may result in the 'out-of-operational-window' issue going away due to the tolerances stacking up differently...

If you don't have gauges, the "poor man's headapace check" method (tape) will work -just make sure to remove the FP and extractor first!

 

[Mike_from_Texas]

I know how to check it, but it says the barrel has to be replaced if it doesn’t check out.

It should be pretty obvious if it doesn’t go into battery.


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[popper]

How do you headspace an AR with a fixed barrel extension?
You don't unless you remove the extension from the barrel and re-install ( not practical!). If you handload, set the sizer for YOUR rifle HS. Or easter-egg the bolts. Lug wear will change it. Check it, if in spec and just using factory ammo, you are OK. Probably OK if it's out of spec anyway.

 

[xsefan]

I had a Rainer arms .308 barrel . It would not head space. Swallowed the no go gaster than Kamal Harris. Shot great for about 1500 rounds. Then quickly opened up to 6 inch groups! Never blew up on me. Wouldn't buy an a2 grip from them . Bad product bad service. This was in 2009 .I had to pay to send It back and pay for return shipping 2 time just to have them tell me it was fine. It went into a lr308 .

 

[Nicholst55]

I realize that I'm kind of late to the party, but I have one caution to share with anyone considering buying headspace gauges for use in Ars or other rifles with plunger type ejectors. Make certain that the gauge(s) you're looking at have a relief notch cut on the base to clear the ejector. If they don't and you use them anyway, you'll get an erroneous reading - the ejector will push the gauge farther into the chamber than normal. That gives you a couple of choices - either disassemble the bolt to check headspace, and then reassemble it afterwards (I'm talking about removing the ejector), or grind a relief notch on your gauge(s). If you don't have a bolt disassembly tool, you'll probably end up chasing the ejector across the room and then trying to find it on the floor. My advice is to either buy the gauge(s) with the relief notch, or grind one on the gauge(s) without them. I post this because after losing all of my gunsmithing tools and gauges to Hurricane Harvey, I just bought some new headspace gauges. You guessed it, the 5.56mm gauges did not come with the relief notch for the ejector!

 

[RiverRider]

How do you headspace an AR with a fixed barrel extension?
You don't unless you remove the extension from the barrel and re-install ( not practical!). If you handload, set the sizer for YOUR rifle HS. Or easter-egg the bolts. Lug wear will change it. Check it, if in spec and just using factory ammo, you are OK. Probably OK if it's out of spec anyway.

Good answer.