Head space

[Danno28]

if I headspace for a 308 round can I safely shoot both 308 and 7.62

[MikedaddyH]

I want to say Yes , But ... It depends on what chamber was drilled(cut) into the barrel. I counted 17 different .308 size bits all ever so slightly different from each other. If you stay away from the military rounds until it is broken in you should be OK. 

[Tripledeuce]

Chambers are REAMED  with a specific reamer  not drilled! 7.62 is just slightly  different than the 308.

  Respectfully

  Terry

Edited December 10, 2015 by Tripledeuce

[MikedaddyH]

Chambers are REAMED  with a specific reamer  not drilled! 7.62 is just slightly  different than the 308.

  Respectfully

  Terry

Terry i was tired it was after 1am....

I want to say Yes , But ... It depends on what chamber was drilled(cut) into the barrel. I counted 17 different .308 size bits all ever so slightly different from each other. If you stay away from the military rounds until it is broken in you should be OK. 

[mrraley]

To answer your question first... NO.

 

this is the what ArmaLite used to say and what I taught in my armorer classes...

 

Is that you can shoot .308 in a 7.62 NATO chamber... BUT you CAN NOT shoot 7.62 NATO in a .308 chamber.

If your AR-10® Series firearm is chambered for 7.62 cartridges, it will fire all standardized U.S.
military 7.62mm cartridges and all factory loaded cartridges in .308 Winchester caliber. Do not
attempt to fire any other cartridges in this firearm. Projectiles between 150 grain and 175 grain
weight provide a good combination of accuracy and functional reliability, with 168 grain
particularly recommended. If your AR-10® Series firearm is chambered for any cartridge other
than 7.62mm, it will fire appropriate cartridges manufactured to SAAMI standards.

 Also you can look in my section Raley's Tech Corner and read ArmaLite Tech Notes...

tech note 45: 5.56 NATO vs SAAMI .223 REMINGTON CHAMBERS, 

tech note 69: HEADSPACE, or 

tech note 96: HEADSPACE INSPECTION. 

 

 

Edited December 12, 2015 by mrraley

[guruofhotrod]

The only place I recall seeing Go, Nogo, and Field Gages for 7.62 NATO is here:

http://www.tothtool.com/Gauges_c_11.html

With some manufacturers offering hybrid chambers on their barrels and as Mikedaddy H explained, their being many different variations

of "308 AR" chambers it would make sense to check headspace with the 7.62 NATO first then, if it won't headspace with those, try

.308 Gages before returning components to their respective manufacturers for assistance. 

 

And mrraley's rule of thumb should be followed:  

 

   "is that you can shoot .308 in a 7.62 NATO chamber... BUT you CAN NOT shoot 7.62 NATO in a .308 chamber."

[jtallen83]

This stuff confuses me, this visual would seem to say the opposite;

http://www.thefirearmblog.com/blog/2015/03/13/graphic-breakdown-of-308-vs-7-62x51/

[guruofhotrod]

Interesting chart but, as some of the commenters on the linked story suggest the details are incorrect:

Jason • 9 months ago

PLEASE do further research on 308 vs 7.62 headspace. This is incorrect internet information presented as fact and sorry to say but the well done graphic here will only help to perpetuate the incorrect information. 
They are correct on #3 that military brass usually has thicker case walls than commercial, but their information headspace and pressure is wrong.
There is a lot of incorrect information on the net about 308 and 7.62 and that was apparently their source of info. Consulting SAAMI and having researched industry standards, shows that they are comparing .308 Win GO headspace against 7.62 NATO NO-GO headspace. Bottom line the ammo is the same size, but the 7.62 NATO has a longer chamber NO-GO. The headspace ranges are overlapping .
Also their pressure data is citing old CUP (copper crusher data commonly called PSI back in the day before they could actually measure PSI) for one and modern piezoelectric transducer actual PSI for the other.

 

McThag • 9 months ago

Welcome to August 2014...

The max pressure for 7.62x51mm NATO is not 50,000 psi, it is 50,000 CUP. 50,000 CUP, in this case, is equivalent to 60,000 psi.

Next, every weapon designed for NATO that fires 7.62x51mm NATO gets proofed with a 140% pressure charge. That's 84,000 psi and the gun must not break to be accepted. That's a pretty sizable safety margin.

The 62,000 psi max pressure for SAAMI is intended to the the absolute limit with a 52,000 psi maximum average pressure.

The differences in headspace has resulted in ruptured cases in some rare instances when .308 is fired in a NATO spec chamber.

Another important difference between .308 and NATO is the leade. Mil guns tend to have longer leades and that tends to lower the actual chamber pressure in the gun. This is for reliability when the gun gets really hot.

I guess the good news is with the ban on importing parts kits with intact barrels, most "7.62x51mm" battle rifles you'll encounter are actually going to have .308 chamber dimensions.

Anecdotally, when was the last time you heard of someones battle rifle blowing up where it wasn't sketchy surplus ammo (which should nominally have been NATO spec to begin with) or a gross error on the reloading bench?

If this was actually a real problem there'd be a lot more broken gun stories out there on the internet because every negative thing in the world gets a thread.

 

DIR911911 .  Zebra Dun • 9 months ago

as I remember it's the opposite , 308 is higher pressure than 7.62 but 5.56 is higher than 223.

Edited December 13, 2015 by guruofhotrod

[jtallen83]

I gathered there were some issues with the graphic but I didn't see anyone commenting on not firing the 7.62 in a 308, just the opposite

"The differences in headspace has resulted in ruptured cases in some rare instances when .308 is fired in a NATO spec chamber."

The pressure doesn't appear to be the issue either.........

When I purchased the barrel for my Matrix build it was marked 308 but the maker assured me 7.62 would function fine in it...

My P716 is marked 7.62 but Sig says 308 is fine........

90% of what I shoot is 7.62 military ammo but I've shot plenty of 308 in all my rifles and never seen any hints of an issue. I use the same cartridge gauge when reloading, can't say I've seen a gauge or dies marked 7.62 x 51???????

I don't doubt the wealth of experience here telling me I shouldn't shoot 7.62 in a 308 but my brain keeps asking why till it understands.........

 

[GRA]

This stuff confuses me, this visual would seem to say the opposite;

http://www.thefirearmblog.com/blog/2015/03/13/graphic-breakdown-of-308-vs-7-62x51/

I have to agree.  It seems I've been told the opposite.

So then, in the Armalite AR10 "DEF10" model, I can fire the .308 but NOT the 7.62x51 NATO, correct?

 

[survivalshop]

Take a 7.62 x 51 round from an american manufacturer & compare it to any american made 308 round & tell me the difference in those case measurements . Head space gages will be slightly different between the two  , of course , but I use a 308 HS gages for all 308 type barrels . I have never seen a commercially available 7.62 x 51 reloading die set & have never used one to reload for my 7.62x51 chambered barrels , in any rifle .

 The NATO chamber differences are for mostly battlefield conditions , dirty chambers from a lot of firing & little cleaning if any . If ammo is loaded in any country that has NATO spec's , the should conform to those specs , but the problem now a days is non NATO countries making so called NATO spec ammo & its not .

 You will not see much 308 ammo loaded to max spec's , so that is a none issue , unless you have a fifty plus year old , shot out ,7.62x51 barreled rifle , that could see some case rupturing . The rifle manufacturers have the "don't use this or that because of liability issues "( cover their behinds , from stupidity ) bad old foreign made ammo & reloader's  who think they know better than the manuals from the ammo manufacturers .

  I shoot & have shot almost 99% reloads from every rifle & hand gun I have ever owned & never a problem . 

[mrraley]

[beantown]

I'm not worried, just as confused, as this normal blonde can be. DPMS marks the LR-308 lowers .308. But from what I have read most new barrels are marked 7.62. Reading what Mr. Raley posted if the barrel is marked 7.62 than .308 is fine to shoot in it. From what I am reading this is correct as the proof pressure of the 7.62 far exceed the max pressure of the .308. It's the head space of a .308 chamber where you run into issues firing a 7.62 in a .308 chambered rifle. Am I following today’s lesson OK???

[shepp]

 

Maybe this thread will help you.

[GRA]

 

Maybe this thread will help you.

Great information here.  Thanks for posting this link.

[mrmackc]

Don't say CAN'T shoot Nato 7.62X51 in a modern  LR308.....308 Winchester....... don't say CAN'T shoot .308 Winchester commercial in a 7.62X51NATO modern rifle.  Just say BE CAREFUL  It has been done years before there ever was an internet or shooting forum.  Pay attention what caliber is stamped on the rifle. My DPMS LR308 has both .308 and 7.62X51 stamped on it.

Use good fresh high quality American or NATO brase cased ammo, don't over heat your barrel with a bunch of rapid fire, and hand load a few notches below the load for .308 Max.found in a brand name reloading manual, use a Chronograph to check the velocity if you are really picky and be sure the rifle is clean and has a good machined chamber. 

Edited December 26, 2015 by mrmackc

[shepp]

I'm not worried, just as confused, as this normal blonde can be. DPMS marks the LR-308 lowers .308. But from what I have read most new barrels are marked 7.62. Reading what Mr. Raley posted if the barrel is marked 7.62 than .308 is fine to shoot in it. From what I am reading this is correct as the proof pressure of the 7.62 far exceed the max pressure of the .308. It's the head space of a .308 chamber where you run into issues firing a 7.62 in a .308 chambered rifle. Am I following today’s lesson OK???

also idk if your being confused by the lower being marked .308, it has nothing to do with the barrel. You could have a lower marked .308 and you could be shooting .338 fed or 7mm08 and so on. It more goes from what your barrel is stamped for. 

 

Maybe im wrong that's just how I take your posts

[beantown]

I understand that if the barrel is marked 7.62 you're good to shoot .308 also. It is confusing for some. And DPMS marking the lower .308 only adds to it. There are quite a few post about it also. I do understand that what the barrel is marked, is what the rifle can shoot. The LR-308 is even speced on the DPMS website as a .308/7.62 rifle. So why not just mark the lower and the barrel, with both calibers, and end the confusion? Then this hit me. Why not make a 7.62 Wylde chamber and end all the confusion?  So much to ponder and so little time to act. LOL

[jtallen83]

Of course I can't find it now but I did recently read about a hybrid 7.62/308 chamber on the lines of a Wylde. I'll keep looking to see where I read about it.........

[bubbas4570]

I know that I will confuse someone with this.......

 

So by the supposed different measurements in the 7.62x51/308 {yer guns gonna blow up world} I should have destroyed quite a few rifles in the past years by taking military brass, resizing it to .308 dimensions, and firing it in 7.62 NATO (along with .308 chambers) chambers....and (this is the CRAZY part) nothing even remotely close has happened.

 

The differences are in the design and metallurgy of the differing rifles, not the ammunition; unless the ammo is at the extreme ends of specifications.

 

The differences in the specs on case measurements between NATO/SAAMI are not the problem, rifle design pressure tolerances are.

[guruofhotrod]

Of course I can't find it now but I did recently read about a hybrid 7.62/308 chamber on the lines of a Wylde. I'll keep looking to see where I read about it.........

That would likely be the chamber that Black Hole Weaponry uses, they refer to it as "308B" :

http://blackholeweaponry.proboards.com/thread/850/308b-chamber

[jtallen83]

That would likely be the chamber that Black Hole Weaponry uses, they refer to it as "308B" :

http://blackholeweaponry.proboards.com/thread/850/308b-chamber

That was the one! Thanks, I was beginning to think I just imagined reading about it.

[survivalshop]

Fulton Armory , Criterion barrels & Maybe even the ones straight from Criterion , also have Hybrid Chambers or sorts . I'm not sure if anyone will tell you what they are cut or reamed at , but they are labeled 7.62x51, but advertised as they will shoot both types ammo . 

[jtallen83]

My Sig 716 is marked 7.62x51 NATO but Sig recommends and tests fires with 308 match ammo. 

[mrmackc]

also idk if your being confused by the lower being marked .308, it has nothing to do with the barrel. You could have a lower marked .308 and you could be shooting .338 fed or 7mm08 and so on. It more goes from what your barrel is stamped for. 

 

Maybe im wrong that's just how I take your posts

like I said verify what is stamped on the rifle,  If the rifle lower is marked 308 that means the lower will accept 308 magazines and since different caliber upper receivers and barrels may be mounted, be sure to  shoot Ammo that matches what is stamped on the barrel and if you want to use a magazine  use a magazine that is compatible with a 308 Winchester cartridge. 

Kind of simple rules, okay?