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Measuring Headspace on an Armalite AR-10


imschur

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  • 1 year later...
  • 1 year later...

one key note about checking headspace is...

 

make sure you use proper gauge for the correct caliber.

 

 

if your rifle is chambered in .308, make sure that they are .308 gauges.

 

if your rifle is chambered in 7.62mm, make sure your gauges are 7.62mm.

 

 

there is just enough difference between the two that using the wrong one, could lead to problems. 

 

 

just remember... you can shoot .308 in a 7.62 NATO chambered rifle, but you can't (not supposed to) shoot 7.62 NATO in a .308 chambered rifle.

you may do it once or twice, but the end result will be bad. anything from a stuck casing to a ruptured chamber.

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Armalite has a wonderful technical brief here on measuring headspace. Obviously it applies to other platforms

Thanks for sharing but when I click on the link I get "page not found" on Armalite's website.

 

The pdf link worked.  Thank you   <thumbsup>

Edited by GRA
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  • 1 year later...

I am told that my G2 DPMS can shoot both.  The 24" Bull barrel is stamped 7.62 x 51(? - without pulling it out to look)

Have not tried 7.62 in it to date, only .308.

Am thinking of getting another upper assembly with 16" barrel to convert to a good bush gun (24" is too heavy and cumbersome for 95% of the hunting that i do), but this whole AR thing is a steep learning curve and I am not sure if other manufacturers parts are compatible with the DPMS stuff.

Any help would be appreciated along these lines.

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  • 5 years later...

I located a set of Go / No-Go gauges - Clymer.   They arrived today.

This is interesting. I'm glad I decided to pursue this.

So I have 3 uppers and one is a KAK .308 barrel with a KAK bolt - The other two are KAK .358 barrels with Bear Creek Arsenal bolts.

On the KAK .308 bolt/barrel combo the No-Go gauge would close... Loose headspacing ?

On the .358 KAK barrels with the BCA bolts, the bolt would close on the Go gauge but wouldn't close on the No-Go gauge - I'm guessing that's how it should be... but it seems like that's what every video I've watched tells me....    But on one of those barrel/bolt setups, it was snug on the Go gauge .... It took a tap with the plastic handle of a screwdriver ... I tried feeding a couple of new .358 cases and some handloaded live rounds and they both fed smoothly with no resistance.

Any input on this would be appreciated - I may try mixing/matching to see if I can get a good proper fit on all three.

Thanks for helping out

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46 minutes ago, BeeKay said:

I tried feeding a couple of new .358 cases and some handloaded live rounds and they both fed smoothly with no resistance.

Those have also never been fire-formed to the chambers.  Never been shot, just reloaded ammo.  You won't know anything until you shoot them, then measure them with a comparator.  You don't know what the chamber is yet, until they go BANG!

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Okay - I have more homework ahead 

But I tried swapping bolt/barrel combos and here's what I got

Barrel #1 )  .308/7.62 KAK  -  Barrel #2) .358 KAK  -  Barrel #3) .358 KAK 

Bolt A) KAK - Bolt B) Bear Creek - Bolt C) Bear Creek

Barrel #1 + Bolt A - Bolt closes on No-Go

Barrel #1 + Bolt B - Bolt closes on No-Go

Barrel #1 + Bolt C - Bolt closes on No-Go

Barrel #2 + Bolt A - Bolt Closes on No-Go

Barrel #2 + Bolt B - Bolt closes on Go - Doesn't close on No-Go

Barrel #2 + Bolt C - Bolt closes on Go - Doesn't close on No-Go

Barrel #3 + Bolt A - Bolt closes on No-Go

Barrel #3 + Bolt B - Bolt closes on Go - Doesn't close on No-Go

Barrel #3 + Bolt C - Bolt closes on Go - Doesn't close on No-Go

So apparently my KAK .308/7.62 Barrel and KAK Bolt are loose in headspacing - not sure how much

The headspace gauges are  - GO 1.630"  -  NO-GO 1.634"

What Next ?

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1 hour ago, 98Z5V said:

Those have also never been fire-formed to the chambers.  Never been shot, just reloaded ammo.  You won't know anything until you shoot them, then measure them with a comparator.  You don't know what the chamber is yet, until they go BANG!

Thank You

There was someone awhile back who posted pics of his bolt and the lugs were all rounded off and chewed up and burred, and the question was Is this normal wear after 200 rounds ?   The reply was "That isn't wear, it's damage"      ... I don't want that to be me after a few hundred rounds .

So I appreciate the help !

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ALSO:  All of the barrels I have have been fired numerous times .  I've fired the .308 barrel the most .

I had all 3 barrels but only one upper and BCG so I swapped the barrels just to try them out and see how it runs... No real issues, but I decided to have a dedicated upper/BCG for each barrel, so I bought some new uppers and now what I have is the set-ups shown above .

The .308 barrel/BCG combo has been fired about 100 times and the two .358 barrels have been fired about 50 times each, using the same BCG as the .308. I'm not seeing any wear patterns that show possible damage.  I haven't measured fireformed brass for stretch yet.

Edited by BeeKay
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