.308 AR Headspace

[Benito]

I was looking at the various .308 AR components I have lying around and decided to see what the headspace is on a Armalite AR-10 bolt and a Ballistic Advantage .308 AR barrel.
The bolt closes on the .308 GO and NO-GO gauges but it does not close on the FIELD gauge.
Would this bolt & barrel combo be safe to use with commercial .308 and/or surplus 7.62 NATO ammo?

 

[EXTREMEPREJUDICE]

Closing on the no-go means it's out of spec. but if it won't close on the field it should still be safe to use.

 

[Benito]

What if any pros/cons are there to such a combo?
Less accuracy?
Case head separation?
More tolerance to fouling and/or ammunition types feeding/chambering?
Extraction issues?
Etc.
Please educate me.

 

[newguy2k3v2]

Reduced brass life if you reload. You will have case head seperations early if you resize fired brass to original spec.

You confirmed what I've seen. An Armalite bolt on a dpms/Kac style barrel will give excess headspace and a dpms/Kac bolt in an Armalite barrel will be too tight.

 

[Benito]

Reduced brass life if you reload. You will have case head seperations early if you resize fired brass to original spec.

You confirmed what I've seen. An Armalite bolt on a dpms/Kac style barrel will give excess headspace and a dpms/Kac bolt in an Armalite barrel will be too tight.

Thanks for the info!
I will make sure to use a DPMS pattern bolt on this. I'm leaning toward Toolcraft.
I just wish there were DPMS pattern bolts out there that had a firing pin safety spring like the Armalite AR-10 BCGs do. I like having that peace of mind, that's all. I might try to see if a DPMS pattern bolt would work inside an Armalite AR-10 carrier, out of pure curiosity. I'll report back when I find out.

 

[newguy2k3v2]

I can say an Armalite bolt works with a Lmt carrier and firing pin.

If you want to get rid of your Armalite bolt let me know. I'm sharing one between a 308 and 6.5 barrel presently and I'd like for each to have their own.

 

[TitaniumBlue]

Closing on the no-go means it's out of spec. but if it won't close on the field it should still be safe to use.

This is simply not true, the NoGo gauge is an arbitrary gauge when it comes to function of a rifle. When a field gauge goes, the barrel is no longer safe. You'd be surprised how many barrels in the semi auto world are spec'd at the "NoGo" length for headspace.

 

[Mike_in_FL]

I was looking at the various .308 AR components I have lying around and decided to see what the headspace is on a Armalite AR-10 bolt and a Ballistic Advantage .308 AR barrel.
The bolt closes on the .308 GO and NO-GO gauges but it does not close on the FIELD gauge.
Would this bolt & barrel combo be safe to use with commercial .308 and/or surplus 7.62 NATO ammo?

In my experience this is how any off the shelf .308 AR barrel will headspace. They don't know if you're going to shoot 7.62 surplus with a larger dimension or not.

Look up how an M14 was chambered. Even my "good" barrel with an M852 cut chamber closes on a 1.634 no go. I only know one person who worked out that his NM M1A has the chamber cut to 1.632 and he will certainly never shoot surplus in it.

 

[Benito]

In my experience this is how any off the shelf .308 AR barrel will headspace. They don't know if you're going to shoot 7.62 surplus with a larger dimension or not.

Look up how an M14 was chambered. Even my "good" barrel with an M852 cut chamber closes on a 1.634 no go. I only know one person who worked out that his NM M1A has the chamber cut to 1.632 and he will certainly never shoot surplus in it.

Thanks for the info.
I am still torn on what to do.
So 7.62 surplus has longer headspace dimensions than .308?
I thought .308 chambers could shoot 7.62 NATO ammo, whereas 7.62 NATO chamber could NOT shoot .308 ammo.
Is this correct?
If so, it seems to suggest that 7.62 NATO has a shorter headspace dimension than .308.
My knowledge on this is extremely rudimentary at best, so please feel free to educate me.

The other concern I have for a longer headspace (closing on the NO-GO) is that as the bolt lugs wear, it will cross into unsafe territory sooner than a shorter headspace (not closing on the NO-GO). Does that make sense?

 

[Benito]

I can say an Armalite bolt works with a Lmt carrier and firing pin.

If you want to get rid of your Armalite bolt let me know. I'm sharing one between a 308 and 6.5 barrel presently and I'd like for each to have their own.

Is it fair to assume that the converse is true, that an LMT bolt works inside an Armalite AR-10 carrier & firing pin????????

Once I figure out what I'm doing going forward, I'll let you know about the AR-10 bolt.

Cheers

 

[Benito]

Bumping this hoping for info/input on LMT MWS .308 bolt compatibility with either the Armalite AR-10 and DPMS pattern .308 bolt carriers.
Thanks

 

[flyer]

FALs are typically headspaced with a No-Go but they have the benefit of adjusting headspace with the locking shoulder. ARs have no way of adjusting short of swapping the bolt or messing with the barrel extension.

I'm having no problems with my 6.5 Creedmoor AR that won't close on a No-Go.

Suggesting that excessive headspace is beneficial in an AR is just silly.

Get the right bolt for your barrel. Mix and match is for people who like breaking guns.

 

[dinmax82]

My BSA barrel and V Seven bolt wouldn't close on a Go gauge. It would chamber a loaded round. Shoots fine. I load up LC brass without any sizing work myself and don't reload them again.