Gunsmithing Aftermarket AR10 barrel headspace issue

[Ishallbie O'Cullkillin]

About 4 years ago, I bought and installed a barrel on an Eagle Arms AR10. The seller claimed it was a barely used Mike Rock 5R, and so far, I have no reason not to believe him. At the time, I didn't have head space gauges, but installed it anyway. I realize that I exposed myself to potential injury or worse, but have only put 200rds down the barrel so far. The rifle puts the 168Amax on steel at 900yds pretty consistently, but the brass coming out of the gun is measuring 1.641" on my Hornady headspace gauge kit. This is longer than the brass that ejects from my Armalite 7.62NATO chrome lined carbine barrel, which measures 1.638".
A 7.62X51mm NATO NO-GO gauge measures 1.6405", so it seems to me that this rifle has excessive head space, and is dangerous to shoot. I'm looking for a way to correct this, but don't know where to start. Should I be looking at the barrel extension? Or is the barrel toast, and I need to replace it?

 

[Ishallbie O'Cullkillin]

So, when my .308 win field gauge (1.638") and my 7.62x51 NATO field gauge (1.6455") show up, and If I do indeed suffer from excessive head space, would I need to remove the barrel extension, shorten the barrel shank, then re-chamber to keep the gas port & extension timed correctly? Gunsmithing costs aside.

 

[Ishallbie O'Cullkillin]

I apologize in advance if I am breaking the "No talking to yourself" rule, but since there are over 100 views, some may find this interesting. I went to a friend's house yesterday and we tried to chamber a .308Win field gauge (1.638") into the above mentioned rifle, using the bolt & carrier from his LR .308. The Bolt lugs are longer, and the field gauge would not chamber, but the go and the no go gauge did.

 

[MikeInUtah]

Just because a no-go gauge chambers doesnt necessarily mean the chamber is unsafe to shoot. None the less, take it to a gunsmith for inspection.

 

[Ring]

no way to change the head space on a AR barrel, as long as the field didnt chamber, its "ok"...
only way you can "try" to decrease the headspace, its try multi bolt heads... but unless you have a box of them, you are SOL,,,

 

[Cascade Precision]

Ishallbie O'Cullkillin, Where in Oregon are you located?
I might be traveling to Salem this next weekend and may be able to swing by if you are between Klamath Falls and Salem.

PM me if you need assistance.

 

[Ishallbie O'Cullkillin]

So I got it figured out. The DPMS bolt & carrier closed on the go gauge, and almost on the no go gauge in the Armalite rifle. I have suspicion that the used Rock 5r barrel was intended for an LR.308. I have 100rds through the gun now with no issues, and have piece of mind concerning the headspace issue. Thanks for all replies. Ogreshooter, I am in Hippie infested, wheatgrass drinkin', tree huggin', gun hatin' Eugene.