My AR-10 project has been work in progress since 2012.  Finally got the last pieces and ran into a problem.





Started to check head space on the high end with Fosters .308 No Go and Field gauges.  Looking good so far.  Then the bolt would not close on Fosters .308 1.630" Go Gauge.  It rotates slightly in extension and stops.  I thought maybe the Go gauge went FUBAR and checked it with a working LMT MWS upper I have and the bolt locked up as expected and did not close on Field or No Go.





Barrel is a Losik 18" mid length Black Nitride finished, stamped "7.62mm NATO 1/10", with DPMS extension.  Purchased from AIM a few months ago.  





Bolt carrier was purchased as new on the EE last year.  It has Black Nitride bolt/carrier key and a NiB carrier that was listed as DPMS compatible.  





So what to do now?  Send it someone to ream the chamber?  Try different bolts?  Replace the barrel?





Never had this problem with any AR-15 builds.





Picture of locking lug area as far as the bolt would go:







 

Does it lock up fully without a gage in it?

Yes it does.

I have a spare JP Enterprise bolt, also DPMS pattern, I was going to try, but it would not work in this bolt barrier.



I don't see why there is this incompatibility as both have gas rings.  The JP was incredibly tight and would not work.

Is your LMT BCG compatible with your DPMS pattern build?

Folks are saying it LMT bolts are DMPS pattern.  Never knew that.





http://www.ar15.com/forums/t_3_121/548076_Accurate__reasonably_priced_308_AR_barrel_with_Armalite_barrel_extension_.html

 

Will the bolt close on respectable top quality Factory ammunition, like federal gold medal match??????

I assume you have removed the ejector and extractor for testing?   Have you tried fitting just the bolt (either one) to the barrel by hand?

Jezus....I just bought one of these barrels.

My barrel checked out just fine

Okay, I was so pissed yesterday that I just put the project aside.  Time for an update.  Some good, mostly bad.
This morning I took the time to examine the bolt carriers and the barrel.  Turns out I have two problems.
The less significant one is the aftermarket bolt carrier assembly.  It appears the tight bolts (LMT and JP) in the new aftermarket carrier is due to the diameter of the corresponding aftermarket bolt tail being 0.001" smaller than the other two.  For those curious, 0.250" versus 0.249" respectively.  I'm guessing the hole in the new carrier is also smaller by the same diameter.  The harder than normal resistance with the LMT and JP bolts start consistently when these tails try to pass through that hole.  All three bolts worked with no problem in the LMT carrier.  
Using the LMT MWS as baseline since it came functional from the factory, all three bolt were tested with head space gauges in an LMT 18" stainless barrel and using the LMT bolt carrier.  I am happy to report all three bolts closed on GO (obviously for LMT), and all three did not close on NO GO or FIELD.  Using a dial caliper, I was able to ascertain that the JP bolt was dimensionally more similar to the aftermarket Black Nitrided bolt.   So the aftermarket bolt carrier assembly is still usable, it just can't easily swap bolts.  Thank god I had invested in the Young Mfg. .308 bolt ejector tool a few years ago.
On the flip side with the Losik barrel, all bolts in the LMT carrier would close on an empty chamber but all would not close on the GO, NO GO, and FIELD gauges.  Conclusion is the barrel does not have enough adequate head space to chamber a cartridge.  This is the major problem and can't be salvaged.  I will be reaching out to AIM this week to remedy this.
 

"Fosters .308 No Go and Field gauges"

"Barrel is a Losik 18" mid length Black Nitride finished, stamped "7.62mm NATO 1/10",

and there be your problem... 308 gage in a 7.62 NATO barrel.

Had the same problem with Forster 308 gage.  

Got Forester 7.62 NATO GO and NO GO and barrel headspaced with no problem.

7.62 chambers are close but they are not exactly the same.  

These are what you need for a 7.62 NATO barrel.

http://www.amazon.com/Headspace-Gage-7-62-NATO-MAX/dp/B008BNY44Q/ref=sr_1_2?ie=UTF8&qid=1444620476&sr=8-2&keywords=forster+7.62+nato

http://www.amazon.com/Forster-Headspace-Gauge-7-62-NATO/dp/B00ZVEIFVQ/ref=sr_1_1?ie=UTF8&qid=1444620476&sr=8-1&keywords=forster+7.62+nato

While checking with gauges, all bolts were stripped of the extractor and ejectors.  All uppers were separated from the lower.
Edited - I think I'm going to do a mea culpa here......the process to barrel a FAL is different with those locking shoulders and can get away with .308 gauges.  The brain isn't what is used to be.



Also the LMT barrel is .308 Win.  Out of curiosity, I stuck a Portuguese round into the Losik barrel and let it chamber normally.  The round actually chambered.  When extracted, it didn't have any signs of damage.



How much force would you apply to a precision gauge?  I certainly would let the full force of a recoil spring slam into the gauge.
Thanks for the Amazon links, I've been meaning to get 7.62 NATO gauges just to avoid confusion.  Ordering today for final judgement.



 

First thing is to get the bolt locking up smoothly.  Oil it up nice and wet and then pull the bcg back with the charging handle and let it slam down and 20-30 times.

That should get the bolt and the lugs in the barrel extension engaging smoothly.

Then it will be easier to headspace it.

Not to hiack this thread but I just assembled a DPMS pattern rifle. I have not checked headspace yet.

My barrel says .308 Winchester on it. I should be checking headspace with .308 gauges, correct?

To clarify.....In regards to ammunition it is opposite of 5.56/.223 pressures. The NATO round has lower pressure than the commercial .308, So if the barrel is marked .308 than I can shoot 7.62mm x 51 and .308. If it is marked 7.62mm x 51 then I can only shoot 7.62mm and not .308. Correct?

It "may" close on a 308 gauge. But not a 7.62 NATO gauge.

Cover the rear of the gauge with 1 layer of scotch tape and try, then maybe 2 layers.  It should not close then. If it dosent you are OK.  There are some YouTube's and info on it. Google it.

New ammunition is significantly shorter than SAAMI minimum and your chamber would have to be very short indeed for it not to chamber. Some new ammo is .010" shorter than SAAMI minimum. This is part of the reason why new ammo grows so much when resizing after the first firing.

Contact the barrel maker. They should be informed about your problem, they will inspect, repair or replace as needed.

Was the bolt disassembled?

Ejector out?

Did you install the extension or have somebody else do it?  If someone else did it, they should have checked it prior to giving it back to you.

If you did it yourself, just have someone with a chamber reamer lengthen the chamber a thousandths or two...

A 7.62 NATO Go gage is longer than a .308 Win Go gage.  If he cannot get a .308 Win GO gage to 'go' a longer  gages isn't going to 'go' either.

7.62 NATO chamber specs are from 1.6355" to 1.6405"
.308 Winchester chamber specs are from 1.6300" to 1.6400"

The essentials are the same for the two chambers, namely the shoulder angle and the reference diameter.

You use 'finger pressure', no more.

Just a note, 7.62 NATO headspace gages and .308 Winchester headspace gages are exactly the same, except being different lengths.  In fact, if you get a complete set of .308 Winchester headspace gages, you wind up with NATO GO and NO-GO lengths. EDIT: I see Pacific Tool has stopped advertising sets of gages in .001" increments between GO and FIELD, I don't know if anyone else does anymore either...

If you overlay a .308 Win Chamber drawing on a 7.62 NATO chamber drawing the only major difference is the throat length.  The NATO throat is about .050" longer.

My continuing saga points to the barrel.



I received the Forster 7.62 NATO MIN gauge listed as 1.6355" today.  The MAX gauge is coming from another source on Monday but appears irrelevant at this point.



The bolt still will not close on this new gauge.



I noticed the round I chambered measures 2.885" OAL.



Taking 10 fresh rounds from the same box they vary between 2.886" to 2.889" OAL.



Chambering the round likely reseated the bullet a hair bit deeper, thus allowing the chambering.

Your bolt is disassembled, right?

The ejector really needs to be out.

Yep.  Didn't bother to reassemble knowing I will be checking again.



 

You removed not just the extractor, but the ejector too, right?

Yes.  Bolt is stripped clean except for gas rings.



I really like the profile of this barrel and am tempted to buy another one from AIM on a chance this one was a fluke.  For the price, it doesn't hurt to have a spare barrel when all said and done.



I bought this barrel back in July, so I have to deal directly with Losok.  However their website is down so I sent an email to AIM for them to get me a way to contact them.



 

Is the barrel removed from the upper?

Barrel was on upper receiver with barrel nut properly torqued to the recommended minimum 35 ft/lb.  It is an SLR Gen4 Solo Light handguard.





 

I would pull the barrel at check again.  Sometimes it's hard to get a good gauge reading with the barrel installed.

It may not result it any different reading but you're faced with swapping the barrel at the moment anyway.

I had already loosened the barrel nut in anticipation this barrel has to be replaced.



Same issue, won't close.

LOSOK contacted me to send the barrel back for inspection.  They will replace it if their gauges confirm this is short.



There website was hacked, hence the dead links.