I'm building an AR right now with a 16" Ballistic Advantage Hanson profile 5.56 barrel and a Lantac Enhanced BCG (nitride finish, full auto-rated, 5.56).  Both parts are brand new, right out of the package.  A few days ago, I installed the barrel in the receiver (a brand new Aero M4E1 Enhanced upper) and torqued it to 45 ft-lbs.  I didn't install the gas block or gas tube because I knew I was going to be checking the headspace (I was waiting on a Clymer go/no-go gauge set to arrive), and I didn't want to waste the roll pins if anything went wrong.  

My Clymer gauges arrived, so it was time to check the headspace.  I cleaned the chamber and bolt face thoroughly, making sure there was no debris (which there wasn't, because it's all new).  Next, I removed the ejector and extractor from the bolt and reinstalled the bolt in the carrier.  The Lantac E-BCG features a domed cam pin, so I re-installed it with the flat face forward, as per Lantac's instructions for proper use.  I inserted the assembled BCG, with the bolt extended, into the upper receiver (without the charging handle), and pressed it forward with my finger until the lugs rotated and the bolt locked, noting the amount of pressure required (not much).  After that, I unlocked the bolt and slid the BCG back in the receiver.  I dropped the Clymer 5.56x45mm NATO "go" gauge (1.4636") into the chamber and made sure it was seated by pressing on it with my fingertip.  I then slid the BCG forward slowly, and watched as the bolt lugs stopped dead about 1/4 into their rotation...  Applying more pressure with my finger on the back of the BCG did nothing to help the bolt finish locking.  This barrel/bolt combo has failed its headspace check.  

I cleaned the chamber/bolt and tried again, with the same results.  I took the gauge out of the chamber and re-seated it -- nothing.  I took the bolt out of the carrier and tried it by hand -- nope.  I took the gauge out and slammed the BCG forward by hand, letting it fully lock a few dozen times, then tried the test again -- no joy.  The lugs just barely begin to rotate, and then everything freezes up.  

I don't have another bolt to try with this barrel (or vice versa), so I can't say for sure which part is the culprit.  Honestly, I'm pretty frustrated.  For some reason, I KNEW this would happen.  That's why I didn't install the gas system when I installed the barrel.  You hear guys spouting off all the time about how you'll never run into headspace issues with new components from well-known, quality manufacturers, but I wasn't about to leave anything to chance.  And here I am, with a barrel/bolt combo that fails the headspace check -- of course.  I'm glad I checked it, at least.  

Here are some photos:

Bolt Closed/No Gauge Inserted:



"Go" Gauge Inserted:



"No-Go" Gauge Inserted:



Maximum Lug Rotation on "Go" Gauge:



Anyway, since I'm not sure which part it is, I'm not sure who I should call:  BA or Lantac.  Either way, with everyone in the country buying up all these parts and manufacturers being constantly out of stock, I have no idea how long it will take me to get a replacement for either part.  It was a nightmare just finding these ones.  Any advice for me, guys?  I was all set to finish the build this week, but that's not happening, apparently.  

Did you reassemble the bolt cam pin?  I was checking headspace and got bad results because the bolt cam pin was not in.  I took it to my gunsmith who pointed out my error.

Yup.  After I removed the ejector and extractor, I reinstalled the bolt in the carrier, inserted the cam pin and firing pin, and replaced the cotter pin that retains the firing pin.  The Lantac E-BCG has a unique "domed" cam pin with a flat edge on one side while the rest of the cam pin head is rounded.  I made sure to orient the flat face of the cam pin toward the front, as per the instructions from Lantac.  Everything was as it should be, and still -- no dice.  

Just curious.  Did you try to chamber a full length sized case or cartridge?  You know, just for S&G's.....

To be honest, I don't have any .223 rounds right now (or 5.56, for that matter).  It's been quite a while since I've owned an AR, so I haven't kept any on hand.  And with ammo flying off the shelves, I was just going to cross that bridge once I built the damn thing.  I'm sure the bolt would probably close on an actual round, since most rounds are going to be a little shorter than a "go" gauge and the lugs look like they're fairly close to fully locking as it is, but something just rubs me the wrong way about building a rifle out of new parts and having it be out-of-spec right from the get-go.  I really want this thing to pass a headspace check for me to feel like I got my money's worth and built a quality firearm, you know?

buy a $45 2nd bolt, just the bolt, to get a "second opinion". consider it a future spare part, or the start of your beater AR build.

I appreciate the suggestion. I may end up doing that if it comes down to it, but to be completely honest, after all the money I've spent on this build, I'm not in love with the idea of spending more, even if it's just 45 bucks for a bolt. I shouldn't have to buy another part (especially if it's not even a part I'm planning to use in the finished rifle), just to test for something that should have been right before one of these parts left the factory. I paid good money for parts that should be within spec, and something is not (unless they're both marginally within spec and I'm just the unfortunate victim of tolerance stacking). A second bolt would certainly help me narrow down whether it's the barrel or the bolt that's at fault, but it shouldn't be the customer's responsibility to keep a whole extra rifle's worth of parts just to figure out the problem when they purchase a manufacturer's component that doesn't function properly.

I've sent detailed (and polite) emails to both BA and Lantac about this issue, so I'm going to wait to hear back from them before I spend any money on extra parts just to get to the bottom of this debacle. Hopefully one of these reputable companies will be willing to work with me and help me sort out a barrel/bolt combo that will pass the headspace check. I'll let you guys know how it goes!

A representative from BA responded to my help desk ticket this morning.  He informed me that BA barrels are checked for headspace and test-fired before shipping, but offered to check my barrel if I sent it in to them.  So far I have nothing but nice things to say about their customer service.  Given that the barrel was checked for headspace at BA, I'm leaning toward the bolt being the culprit.  I am still waiting to hear back from Lantac.  I think the best course of action, at this point, would be for me to see if I can have Lantac send me a replacement/spare bolt so that I can run the headspace check again.  Again, even if the original Lantac bolt was within spec, it could just be a tolerance stacking issue.  If a new bolt does not solve the problem, I will probably send the barrel in to BA to have it checked.  I'll keep you guys updated.

just an FYI, different brands of headspace gages yield differing results.  I have PTG, Clymer, and Forster HS gages (sets), and on a borderline setup, the different brands yield different conclusions.

So, given that it seems pretty close to locking, I'm wondering if it might be worth it to try letting the bolt slam home a few dozen times on the empty chamber, under spring pressure from the buffer spring.  If there's a bit of a raised edge on one of the lugs on either the barrel extension or the bolt, this might smooth things out and create enough clearance to allow the bolt to finally close on the "go" gauge when I test it again.  My only fear is that doing so might create wear marks on the BCG or bolt, and Lantac might not want to exchange it for me if it still doesn't pass after that.  What do you guys think?

I was going to suggest this.  Sometimes, like a new pair of shoes, shit needs breaking in.

Tried it out, but still, no dice...  Such a bummer, man.

Like others have said, too bad you don't have a spare BCG to test.

Yeah, I wish I did... We'll see if Lantac will help me out. I might try a different set of gauges in the meantime, if I can get my hands on any.

Or maybe a cartridge...just for the hell of it

For AR bolts, I always thought the critical dimension concerning headspace was the distance between the rear of the lugs and the counterbore of the bolt face. For 5.56, I believe 0.156" is the spec with a minus only tolerance of 0.003" (0.153"). Easier to measure without the extractor, but doable with. Checking the trueness of the rear of all the lugs is a bit harder to do.

That's good to know, but unfortunately, I don't have a readily available means of measuring that distance with that degree of accuracy.

I've got a set of Forster gauges coming -- a .223 Remington GO/FIELD combo. I went with the .223 set because Forster's 5.56x45mm NATO set features a MIN gauge (1.4636") and a MAX gauge (1.4736"). While this MAX gauge length is military spec (essentially a military FIELD gauge), I don't find it especially useful. Their .223 set features a 1.4636" GO gauge and a 1.4696" FIELD gauge. These lengths are identical to the lengths of Clymer's 5.56 GO/NO-GO gauges. While a 5.56 chamber with a bolt that closes on a .223 FIELD gauge might stay open on a 5.56 MAX gauge and thus be technically "within spec," it would have a much shorter service life. I personally believe that a new barrel/bolt combo should not close on a .223 FIELD gauge in order to be considered acceptable. The FIELD/NO-GO gauges aren't really relevant to the headspace issue for this barrel/bolt combo, but that's my reasoning for selecting the Forster gauges that I chose, in case anyone cares.

It does seem likely that your chamber is reamed at the short end of spec, as with the bolt counterbore.
An option that I would choose for this scenario would be to polish the chamber. Some Flitz, a 30-35 cal bore mop. section of cleaning rod and a cordless drill works pretty good. You won't remove much material but it may help. You should stay out of the leade and rifling by plugging it with a bullet dropped in from the chamber or a dowel down the bore and clamped to the muzzle. The focus in this situation would be at the datum point (0.330") of the chamber, which is between the neck and the shoulder. If you do this, make sure to thoroughly clean the bore and chamber when done. Some people polish chambers on new barrels as a standard procedure for all builds.

Well, I'm officially stumped...  Here's an update on my situation:

I spoke to technical support at Lantac, and they were kind enough to generate a shipping label for me to send the BCG and the barrel to them so that they could try some different bolts and find one that passed the headspace check for me.  I sent the barrel and BCG in to them, and I just got a call from them about it.  After receiving the parts, they performed a headspace check and said that my barrel and my bolt passed both the "go" and "no-go" tests.  They said that they used two sets of gauges to double-check, and even installed a different bolt in the BCG to check against my barrel, and that passed, too.  They even installed the barrel in an upper and checked with the BCG in the upper, and it passed.  So, they're sending the parts back to me (and were even kind enough to send along an additional spare bolt that I requested as a backup, and purchased).  

I don't quite understand why the barrel and bolt weren't passing when I was testing them...  I literally performed the test dozens of times, to no avail.  Every single time, the lugs would begin to rotate and then stop about 1/3 of the way through their rotation, short of fully locking.  This was with a new Clymer 5.56 "go" gauge, and then I tried again before sending it out to Lantac, with a brand new Forster .223 "go" gauge (both 1.4636").  No matter which gauge set I used, it failed the "go."  Lantac said that they used a PTG gauge for the first test, and then checked again with an incremental gauge set.  So I'm at a loss for what the issue was when I was running the test...  The only difference I can think of between what I was doing and what Lantac said they did was that I was testing my barrel installed in my upper, and the barrel was an extremely tight fit in my upper.  I don't think that would really make much of a difference, though.  

Any thoughts?

Just shoot it!

I plan to, but I'm the type of person that doesn't like unsolved mysteries.  This is going to bug me until I can figure out WHY I could never make this thing pass a headspace check and the guy at Lantac could on the first try...

Are you performing your test without a charging handle?  If so, why?
Eta: I guess it doesn’t matter.

As others say, just shoot it.  BTW, you can test headspace without assembling the upper.  Just drop in the gage and insert the bolt and see if it will rotate.  If it does on the go and not on the no go, you’re good, assemble the upper.

That was a little bit of text that I shouldn't have included in my original post.  I did initially perform the test without the charging handle because I wasn't thinking and I didn't want the resistance of the charging handle latch to give me a false sense of bolt resistance when performing the test.  Once I reminded myself that I could simply push the charging handle forward and "pre-latch it," and that having the charging handle would be beneficial in case the bolt lugs got a little sticky, I performed the test with the charging handle.  Sorry for the confusion.

I am aware that you can check headspace without the barrel installed in the upper.  It was a while before my gauges arrived, and I had test-fitted the barrel in the upper before then, so I went ahead and did the test with the barrel installed because I didn't think it would make a difference.

I wanted to mention something that illustrates how tight the headspace was for me, since it's one of the things I can't stop thinking about whenever I think about this issue.  Out of the 50 or so times I tried the headspace check, the ONLY time I was able to get the bolt lugs to rotate further than halfway with the gauge in the chamber was when I put considerably more pressure against the back of the BCG with my hand than I had when I initially pushed the BCG forward on an empty chamber to test the amount of pressure required to lock the bolt closed before I performed the "go" test.  I was not very comfortable doing this, because I know you're not supposed to force anything during a headspace check, but I decided to try more pressure once just for the hell of it since I had tried everything else and I wondered if perhaps the new parts were just a little "sticky."  

When I did this, the lugs rotated only a hair further than they had before, and the bolt still did not lock closed.  Doing this, however, caused the bolt lugs to freeze up so tightly against the barrel extension lugs that I couldn't even get the BCG to release rearward by pulling on the charging handle as hard as I could.  I actually had to place a plastic rod up against the underside edge of the carrier at a rearward angle and tap it repetitively with an armorer's hammer just to get the bolt lugs to free up/rotate and allow the BCG to slide back to the rear.  Trying the test again after that (with normal pressure) just resulted in the same failure to pass.  This is why I'm so amazed that the guy at Lantac was able to get a passing "go" test result.  I just don't understand how this barrel and bolt were so tight in my hands but apparently performed perfectly for him.  Based on what he told me on the phone, the "go" gauges he used have the exact same dimensions as the gauges I used.  I'm just bewildered...

You could always send your gauges to Lantec and let them check to see if they have a difference result.

Yeah, I was considering that.  Unfortunately, I think they've already packed up the barrel and BCG to ship back to me.  It might already be in the mail...  If I get them back and they still don't pass when I perform the headspace check again, I might send them back, on my dime, with my gauges, to see if they'll look into it further.  My gauges are brand new and I'm betting theirs are not, so if there's still a discrepancy, the two possibilities are that both my brand new gauges were made to the wrong dimensions, or theirs have been worn down a little.  Either way, it's worth it to me to investigate further, if they're willing to help.  This is going to drive me crazy until I figure it out.

Someone suggested this to me and I'm skeptical, but curious about it.  Could the fit between an upper and a barrel be so tight that it could slightly alter the dimensions of the chamber enough to affect headspace, assuming that both the barrel and the bolt are close enough toward the edges of their tolerance ranges that they just barely pass prior to assembly?

For anyone who cares, here's an update on the headspace issue:

I got the barrel and BCG back from Lantac, along with the spare bolt I purchased from them.  I stripped the ejectors and extractors off both bolts, made sure everything was clean, and then ran a headspace check with each of them on the bare barrel with my Forster "go" gauge.  The new bolt passed just fine -- bolt lugs rotated fully behind the barrel extension lugs for a full lockup.  However, no matter how many times I tried it, the old bolt still failed the headspace check in this barrel.  Again, the lugs would only rotate about 1/3 of the way behind the barrel extension lugs before they'd freeze up tightly and refuse to turn any more.  Here's a pic:



I decided to investigate further, so I tried each of these bolts with a brand new 11.3" BA Hanson barrel that I was able to get my hands on while these parts were off at Lantac.  Both bolts passed the headspace check with this barrel.  In fact, the bolt lugs rotated even more smoothly/loosely with this barrel than the bolt lugs on the new bolt did with the 16" barrel when it passed.  Based on these results, I've decided that the 16" BA barrel must be right on the edge of its tolerance range, to the point where the tolerances on the old bolt and barrel stack up just enough to fail by a hair with my "go" gauge.  Both parts seem to be in spec, but for whatever reason, this particular combination of this barrel, the old bolt, and my gauge doesn't pass.  I'm sure that the old bolt will still close on a live round with this barrel, so I'm not really concerned with it from a safety standpoint.  I bet this barrel/bolt combo would pass the headspace check just fine after I've put a few hundred rounds through it, and even if it doesn't, I now have a second bolt from Lantac that passes anyway, so it's no big deal.  At least I finally figured it out!

Good to hear the new bolt passes the gauge test. I'd use the new bolt with that barrel and get a good night's sleep tonight.

Why would you use an old bolt with a new barrel?  Drop the old bolt in the spare parts bin.

I think you're a little confused about what I meant when I used the word "old."  Both bolts are new.  My whole original post was describing how a brand new bolt and a brand new barrel failed a headspace check.  I purchased the first bolt about a month ago to use with this new barrel, and then I purchased another one from Lantac about a week ago.  Neither one of them have seen live fire.  I used the words "old" and "original" to distinguish between the new bolt that I sent in with the barrel to Lantac for headspace inspection (i.e., the one I checked that failed) and the second new bolt that I purchased from Lantac while they were inspecting the first new bolt and barrel (i.e., the one that I wasn't able to check myself until they sent all the parts back just the other day).  Hopefully that clears things up.