[Joshua13]

Ok so apparently the American version is stamped 7.62 and the Canadian version is stamped .308
Did they change a bunch of stuff to allow for civilian higher pressure loads? Or can the American version also handle those even though technically you shouldn't use .308 cartridges in a 7.62 chamber due to pressure

 

[haugrdr]

If you stick to SAAMI you pretty much can't go wrong. YMMV.

Kel Tec says the RFB can use both...in either country.

 

[Junkie]

Given the adjustable gas system I imagine you'll be ok with either as long as you have it adjusted reasonably. If you have it adjusted for Tula and you shoot really hot stuff I doubt it'll appreciate it...

 

[dave_mishchenko]

My understanding is that the difference in caliber marking used to make it easier to export from the US.

 

[BlakeHanson]

My understanding is that the difference in caliber marking used to make it easier to export from the US.

I believe this is absolutely correct. It's silly regulations. The 7.62x51 is a designation for a military cartridge, .308 is civilian.
You just can't be importing "military assault weapons"!!!

Strangely missing from the SAAMI specs, is the 7.62 x51.

I looked closely at the 2 cartridges and almost all gunmakers say you can use either one. And you can.

So what's the difference???

The 7.62x51 is designed to be used in a machine-gun and has a thicker walled case to withstand the abuse of high cycle-rate fire and being in a 'chain'.
That also meant it had less room for powder and more expensive brass.
When they "civilized" it into the .308 they didn't need the expensive thick brass cases and would prefer room for a little more powder.
The increase in pressure for the .308 was still within the test tolerance for 7.62x51 so why not?

The main point is, the .308 case is less rugged to abuse than the 7.62x51.
So you can't link a bunch of .308 ammo together and feed it to a M60 machine gun. The cases would get bent.

KT puts 7.62x51 on the US RFB's because the case can stand more abuse and is less likely to fold up and break something like, oh I don't know, say an extractor. Guess which one they would prefer us to shoot with a lifetime warranty on the gun?:headstratch:

In a nutshell: Can we use either in our RFBs interchangeably? Yes.

But you can't use .308 rounds to do this:
https://youtu.be/Clv82A8Mgzg?t=1m18s

 

[ronmar]

There is no real pressure difference. What confuses people are the units.. The .308 spec is in PSI, the 7.62 being done for the gubmnt is in CUP. Some older milspec chamberings like 30-06 are also specced in CUP. People see the Xx thousand number and assume it is in PSI but it is not. CUP stands for copper unit pressure where they measure a carefully sized copper disc that gets crushed in a test fixture during the shot. The ammount of crush equates to a chamber pressure. Back in the day before they could measure the shot pressure directly, that was how it was done. Converted to PSI, the CUP spec and the PSI spec are very close.

The biggest difference in the two rounds is as noted for durability the case wall is thicker, and because of that the milspec 7.62 runs a lesser powder charge than the comparable velocity .308 loading. The chamber spec for 7.62 is also looser for reliability over accuracy. It seems to be a closely guarded secret. I have never been able to find a reliable spec for the 7.62. At any rate, the two have always been interchangeable.

As for the differences in the canadian model RFB. Well I think that ends with the lack of muzzle threads and the .308 stamp. I would bet they have the exact same chamber, reamed to whatever chamber spec KT decided was 7.62

 

[Joshua13]

Why then does sammi say do it use 7.62 in .308. Yet if fails to mention the other way around.
The whole issue came up because I was just using my uncles new ,(-200 rnds) Springfield m1and we got three fail to eject and when we opened the action the third time pieces fell apart. We assumed it was from too much pressure using .308 cartridges

 

[henshao]

I can see how that might seem like the culprit but people have been running either through guns chambered for either, for eons.

 

[BlakeHanson]

There is no real pressure difference. What confuses people are the units.. The .308 spec is in PSI, the 7.62 being done for the gubmnt is in CUP. Some older milspec chamberings like 30-06 are also specced in CUP. People see the Xx thousand number and assume it is in PSI but it is not. CUP stands for copper unit pressure where they measure a carefully sized copper disc that gets crushed in a test fixture during the shot. The amount of crush equates to a chamber pressure.

The earlier 7.62x51 pressure specs were in CUPs.
When it became 7.62 NATO, the spec is in PSI.
The max recommended pressure is listed as 60,190 PSI by NATO testers and 75,275 PSI for the proof round.
(remember NATO still has some countries using Vietnam era M60s).

SAAMI's pressure specification for the .308 (for us civilians) is 62,000 to 66,000 PSI.
This is less than half way from maximum recommended pressure and the proof pressure of the 7.62x51 ; it only amounts to a maximum of +10%. You can see how they can say it is safe to shoot either one in either.
As stated, no 'real' pressure difference.

This would not have caused an M1 Garand to fail. Remember, it fired a proof round at the factory at 75,000 PSI. If anything would have broken, it would have been then.

 

[Junkie]

The issue with the Garand is that with hot commercial loads it's WAY overgassed, which is why they can bend oprods. If you solve that problem (there are various solutions), it seems to be ok with hotter ammo.

 

[marukka2]

One difference no one else has pointed out is headspace. NATO STANAG 2310 specifies 7.62 NATO headspace as 1.632 - 0.006, SAAMI specifies 308 Win headspace as 1.634 -0.007, my Forester 7.62 NATO gages are for some reason different from the STANAG iirc. If you want a copy of the STANAG you can get it here:

https://drive.google.com/open?id=0B2MvE3Rweb__TVEyRktWazJvbUU

Why then does sammi say do it use 7.62 in .308. Yet if fails to mention the other way around.
The whole issue came up because I was just using my uncles new ,(-200 rnds) Springfield m1and we got three fail to eject and when we opened the action the third time pieces fell apart. We assumed it was from too much pressure using .308 cartridges

I would assume so, the Hornady reloading manual has reduced power "service rifle" loads for the M1A/M1 Garand. I'm pretty sure there are aftermarket gas blocks which allow you to bleed excess pressure as well.