Build Thread I know, dont fire 5.56 from a .223. Does the same apply for a .308 and 7.62x51??

[FireArm]

Im building an AR10 from Palmetto State Parts. The lower is complete and I am ready to purchase my upper. I want to be able to fire both .308 and 7.62x51 caliber rounds from the rifle. Which of these calibers should the rifle be chambered in for me to be able to do that?

Read More

 

[ChiefStealth]

Generally accepted that you should not shoot .308 from a 7.62 chamber. You can shoot both .308, and 7.62 in a .308 chamber. If you want to shoot both, get the .308 chamber.

 

[FireArm]

Any suggestions for barrels and best twist rate for these two calibers?

 

[JRuby]

The bullet is the same for both. I believe 1:10 is pretty standard for .308 but you may have plans for something specific and a specific twist may be more beneficial. I know nothing of AR 10's but have a fair amount of experience with 30-06 and other 308 caliber rifles.

 

[Boboclown]

Despite what is "common knowledge" you can shoot .308 in a 7.62 NATO chambered rifle. The "issue" is that the headspace for 7.62 NATO is longer, which means that if you intend to reload then don't use .308. Other than that rifle will be fine.

Twist rate is up to you. If you only intend to shoot between 147 and 168 (175 may or may not be good depending on ammo) then 1:12 is fine. Any heavier and you'll want to look for a 1:10.

 

[mjbskwim]

Generally accepted that you should not shoot .308 from a 7.62 chamber. You can shoot both .308, and 7.62 in a .308 chamber. If you want to shoot both, get the .308 chamber.

Never heard such nonsense
I have shot both from both rifles and never a problem

 

[Medic!]

Im building an AR10 from Palmetto State Parts. The lower is complete and I am ready to purchase my upper. I want to be able to fire both .308 and 7.62x51 caliber rounds from the rifle. Which of these calibers should the rifle be chambered in for me to be able to do that?

I find it funny that 7.62 is a military designation.
Yet both the HK-91 and Belgian FN FAL are stamped .308 on there receivers.

Anyhoot. Here is some more fuel for the fire.

Fulton Armory: What's the Difference between .308 Winchester & 7.62x51mm NATO?

 

[titsonritz]

It is the opposite of .223 vs 5.56x45...

.308 Winchester vs. 7.62x51mm NATO

 

[Medic!]

I here what your saying titsonritz.

But I think I'm with mjbskwim on this one.
I'm not compelled to worry much about it.

The G-3 and FAL were used by most of the ''Free World''. And they were made for 7.62.
But there original makers had no problem also stamping there receivers .308.


Your link if anything puts my mind to rest.

.308 Winchester vs. 7.62x51mm NATO

 

[wired]

Ive been dumping 308's into 7.62's and the other way around for 30 years . Non issue.

 

[mjbskwim]

The main thing is a quality barrel with a strong chamber.
The Mini 14 is marked 223 but the Ruger website says no problem with 556. So they made the barrel with a chamber strong enough to handle 566.
Do the same thing with your build. Use top quality parts and you shouldn't have any problems

 

[11Charlie]

Totally agree with @mjbskwim and the others. Use top quality parts and your fine. I have shot both from my AR-10 with no issues what so ever.

 

[USMC-03]

Twist rate is up to you. If you only intend to shoot between 147 and 168 (175 may or may not be good depending on ammo) then 1:12 is fine. Any heavier and you'll want to look for a 1:10.

Ideally if you're going to be shooting over 168 grain bullets out of a 308 a 1:11 twist is perfect; a 1:10 really isn't needed until you get over 200 grain and the 308 then just doesn't offer the case capacity to make that weight class shine. Also go for an odd number of lands and grooves; lands 180 degrees from each other add stress to the bullet and offsetting them can dramatically improve performance.

 

[Boboclown]

Its not about chamber pressure with the .308 and 7.62 NATO (the difference, if any, is negligible), just a longer chamber not being ideal for the thin case. So pretty much a non-issue.

 

[IronMonster]

For what you are doing, I agree its a non issue.

However I have an old FR8 Cetme chambered in 7.62X51 that I wont shoot .308 out of. Its one of those things that is marginal to begin with and there are a few reported failures using .308 ammo so better safe than sorry.

In a new manufactured AR or other modern rifle I wouldn't think twice about it.

 

[Boboclown]

However I have an old FR8 Cetme chambered in 7.62X51 that I wont shoot .308 out of. Its one of those things that is marginal to begin with and there are a few reported failures using .308 ammo so better safe than sorry.

If you don't mind me asking for sake of clarification, were these failures from both the FR7 and the FR8, or just one of the two?

 

[IronMonster]

If you don't mind me asking for sake of clarification, were these failures from both the FR7 and the FR8, or just one of the two?

I honestly dont know. If I recall the issue with these was that some early ones where chambered in what they called 7.62 x 51 Cetme which was the same cartridge specs but loaded wimpy (light even for a 7.62 x 51) and that the stretch from that to a hot .308 round is just too much in some cases.
I am not an expert in them by any stretch.

 

[mjbskwim]

I honestly dont know. If I recall the issue with these was that some early ones where chambered in what they called 7.62 x 51 Cetme which was the same cartridge specs but loaded wimpy (light even for a 7.62 x 51) and that the stretch from that to a hot .308 round is just too much in some cases.
I am not an expert in them by any stretch.

Boy the only problem I have ever had from my CETME was trying some soft point hunting rounds I got cheap.
Those just wouldn't feed.
Spit everything else right where I pointed the gun and threw the cases into the next county

 

[IronMonster]

Boy the only problem I have ever had from my CETME was trying some soft point hunting rounds I got cheap.
Those just wouldn't feed.
Spit everything else right where I pointed the gun and threw the cases into the next county

Well, we are not talking about the same thing. The Cetme G3 pattern semi auto rifles where all chambered in 7.62 x 51 NATO I am pretty sure. The Cetme I am talking about is a reworked Mauser 98 bolt action rifle.

 

[Boboclown]

I honestly dont know. If I recall the issue with these was that some early ones where chambered in what they called 7.62 x 51 Cetme which was the same cartridge specs but loaded wimpy (light even for a 7.62 x 51) and that the stretch from that to a hot .308 round is just too much in some cases.
I am not an expert in them by any stretch.

Its the FR7 then. The FR7 is a small ring mauser while the FR8 is the large ring. The FR7 was chambered for their weak 7.62x51 CETME, the FR8 was chambered for 7.62 NATO. Never heard of issues with the FR8, but I have with the FR7 and commercial .308.