Measuring Headspace on an Armalite AR-10

[imschur]

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

[44Dave]

Brownells has a few different brands listed.  Do we like any one brand better than the other?

[survivalshop]

I have a couple of different brands , as far as I know they all work , but we have to trust the manufacturer to keep to HS gage spec's.

[mrraley]

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.

[blue109]

Sure you don't have that backwards?

[wetncold]

My thought too.

[mrraley]

If you look through the attachments,

 

you will notice the key .308 dimensions are just thousandths smaller than the 7.62.

 

and in a properly cut chamber, it only takes a thousandth to throw anything off a little.

[jtallen83]

I keep reading about a hybrid chamber that works for both?

Does this follow the same principle as the Wylde chamber for .223?

I'd like to shoot both if possible

[mrraley]

I only have one on that currently. but it covers a wide selection.

 

but the wylde chamber is big enough to cover both NATO and SAMMI.

223-556 Reamer dimensions.pdf

Edited July 2, 2015 by mrraley

[GRA]

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 July 3, 2015 by GRA

[mrraley]

ArmaLite has taken all information off the web site as of recent. 

 

I have been trying to put as much as I can back on here in order to help as much as I can. 

[broadbillodin]

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.

[Matt.Cross]

Long answer short, you'll have no trouble shooting either in your platform. Go for it!

[BeeKay]

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

[98Z5V]

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!

[BeeKay]

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 ?

[BeeKay]

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 !

[BeeKay]

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 January 10, 2023 by BeeKay

[BeeKay]

 Hey,  Sorry - I ended up making those posts here because I thought this was a thread that I started 

We had some power failures here over the past 3 weeks and it caused confusion.  But there's good info here anyhow

Not trying to hijack this thread