AR 15 headspace


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jelenko
February 17, 2012, 10:56 PM
I just rebarreled by AR 15. The fired cases are coming out 3-5 thousands larger than the earlier barrel.
The bolt is the same.

That means the chamber in the new barrel is 3-5 thousands larger than the previous one - yes?

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dprice3844444
February 17, 2012, 11:25 PM
change bolt face

rcmodel
February 18, 2012, 11:38 AM
Larger in diameter?
Or longer headspace?

If larger in dia, you have a looser chamber in the new barrel.
If longer in length to the shoulder, you have more headspace in the new barrel.

Did you check the set-up with GO and NO GO headspace gages when you put it together??

rc

jelenko
February 18, 2012, 03:30 PM
It's longer - checked with RCBS precision mic.

The fired cases are coming out +2 to +4 on the mic.
Fired cases from the previous barrel [with the same bolt] came out - 1.

I'm not too concerned since I resize the cases to ~ -2 thousands from the fired case size.

I just wanted to make sure I've got it right that it's the new chamber that changed and not some way that the bolt was locking up in the barrel extension.

xfyrfiter
February 18, 2012, 03:51 PM
Is the bolt new also? If not then you really should have the headspace gauged with go-no-go gauges, if it is a new bolt you should be ok but I would check anyway just for safety sake. A ka-boom next to your face is just not very pleasant.

rcmodel
February 18, 2012, 04:00 PM
I'd be in favor of putting a new bolt in it to go with the new receiver extension.
First, the wear pattern on the old locking lugs are not going to match the lugs in the new barrel extension.

And by the time an AR needs a new barrel, it needs a new bolt too.

Just a matter of time until it cracks a lug.
Or breaks in two at the cam pin hole.

Then you got a real problem to deal with.

rc

rskent
February 19, 2012, 05:53 AM
Good advice Most people I know keep the bolt with the barrel. When you change barrels
you change bolts. When you put the barrel on another gun or sell it the bolt goes with it.
Steve

jelenko
February 20, 2012, 08:43 AM
Hmmm. I change barrels about every 3-4 thousand rounds. The bolt has been in two previous barrels - but it has only about 6000 rounds through it.
Are you really saying that a bolt only lasts about 4 thousand rounds?

rbernie
February 20, 2012, 08:47 AM
Are you really saying that a bolt only lasts about 4 thousand roundsWe had a recent thread on this:

http://www.thehighroad.org/showthread.php?t=644284

Considering that the bolt is a $70 part, it's probably wise to replace it with each new barrel from a cracking perspective. I was always taught to replace it with each new barrel from a wear/headspace perspective.

Taurus 617 CCW
February 20, 2012, 09:20 AM
Take it to a shop that has a set of headspace gages and have them verify the headspace. If you replace the bolt, have the headspace verified also.

jelenko
February 22, 2012, 05:55 PM
Ok. Changed the bolt, no change in size of fired brass.
Since the fired brass all is well within SAMMI specs [as measured by the RCBS precision mic], I'm not concerned about headspace.

If we could return to the original question. Given that the bolt is the same, if the brass comes out longer, it must be the chamber in the new barrel - yes?

rcmodel
February 22, 2012, 07:32 PM
Yes.

rc

Jim Watson
February 22, 2012, 08:37 PM
There was a guy here who felt similar anxiety when his fired cases showed a few thou longer in the RCBS gadget than he liked. The rifle was brilliantly accurate, much better than I would have expected out of a 3-gun AR, but he could not stand it and pressured the company for a new barrel. He got one with no excess headspace but it was not as accurate as the slightly sloppy original. Oh, well.

jelenko
February 22, 2012, 10:23 PM
Thanks!

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