7.62x51 and 308

[Coleg749]

Are 308 and 7.62x51 interchangeable. I have a mossberg mvp patrol. Could I shoot both 308 and 7.62 in it? Also, when reloading, can I use 7.62 cases

[PA Patrick]

I was told .308 in 7.62 NO but 7.62 in .308 was ok. I do know the differences in cases are .013 on the neck. I would stick with what is stamped on the barrel.

[TMD]

About as different as 55.56 / .223. Same dies, same bullets. And before the Internet there was never an issue.

[cryogenic419]

I thought you could shoot 7.62 in .308 chambers but not the other way around.

.308 was supposed to be a higher pressure round

[Mobuck]

"I thought you could shoot 7.62 in .308 chambers but not the other way around.

.308 was supposed to be a higher pressure round"

Generally, yes. The problem is some older "expedient" conversions of existing military rifles. Some of those conversions were questionable(bordering on just plain dangerous) and commercial .308 Win may cause serious problems.
I feel confident that any modern(current production) firearm will handle any cartridge that will fit in the chamber-at least it won't explode in your face.
This is relating to the .308/7.62. I don't want to start an argument about .223/5.56.
Oh yeah, forgot the question about cases. Externally, cases are the same after resizing. Follow your reloading manual's recommendations about reducing charges in military cases. I've hit max loads as much as 2 grains lower with military cases(especially European) vs domestic commercial brass.

[USMC 77-81]

In a bolt gun of current manufacture I wouldn't hesitate to shoot .308 in a gun marked 7.62 x 51 but would be a little cautious in an auto loader due to the action cycling milder or harsher depending on operating pressure. I have shot commercial .308 through my M1A without problem before I started reloading. I will state though that since I began reloading my powder of choice has been IMR 4064 and the M1A cycling is oh so smooth!

[T. O'Heir]

"...And before the Internet there was never an issue..." Thank you. Been saying that on assorted forums for years. Applies to the bullet weight damaging a rifle too.

[Unclenick]

I was told .308 in 7.62 NO but 7.62 in .308 was ok. I do know the differences in cases are .013 on the neck.

I thought you could shoot 7.62 in .308 chambers but not the other way around.

.308 was supposed to be a higher pressure round

All rumors. Here's how and why it got started:

The 7.62 NATO cartridge was a military development adopted by Winchester under the .308 Winchester name a couple of years later for the civilian market. The NATO cartridge at the time of its development had a peak pressure of 50,000 CUP, as in the M80 spec, but which is reported as 50,000 psi in the tech manuals, causing the initial confusion.

Later, European NATO developed M993 AP with a pressure of 380 MPa, or 55,115 CUP, but also reported as "psi" in the U.S. military tech manuals.

When SAAMI got reference loads from the military, they measured 52,000 CUP, which they reported as CUP. So the SAAMI number for commercial cartridge peak pressure was actually right in the middle of the military range of 50-55 kpsi. The 2000 CUP difference from the original 50,000
CUP military measurement was due to the SAAMI copper crusher being a little different from the M11 military copper crusher. It's not a significant difference in a copper crusher results, as copper crushers are notoriously imprecise in the first place.

And then SAAMI switched from copper crushers to conformal piezoelectric transducers and the rumors started to get serious. The exact same load that measured 52,000 CUP in a SAAMI copper crusher, measured 62,000 psi in a SAAMI conformal piezo transducer, which SAAMI reports as "psi" to keep the result distinct from copper crusher results in CUP.

Now you see the problem. Because the military reported copper crusher results as "psi" the rumor mill compared that to the piezo reading made by SAAMI reported as "psi" rather than comparing it to the SAAMI CUP number, which they should have done to be apples-to-apples, and that made everyone think the SAAMI pressure was higher. In reality, it was all just an artifact of different measuring methods being employed.

Today the military also uses piezo transducers, but two different kinds, depending which side of the pond you live on. The U.S. uses the SCATP 7.62 standard which employs the same conformal piezo transducer SAAMI uses, and loads to the same 62,000 psi that SAAMI measures on this instrument. The NATO allies use a tunnel transducer per the EVPAT standard, and report 60,190 psi (actually, 415 MPa). Here again, the small difference of under 2,000 psi difference is just due to measuring system differences. The military here provides the reference loads to NATO for the cartridges developed here, so you know this is just different machines disagreeing a little about what the pressure value actually is.

As to the cartridge dimensions, there are some very minor differences. The military max COL for this cartridge is 2.800" where SAAMI uses 2.810". The military case length tolerance is -0.015" from maximum, where SAAMI allows -0.020" from maximum. The head to shoulder datum tolerance is -0.007" for SAAMI and -0.006" for the military. SAAMI allows diameter tolerance of -0.008" while the military allows -0.007". But all those differences in tolerances are as subtracted from the same maximum values.

In chambers, the military minimum chamber is 0.002" longer and their FIELD REJECT gauge, is, I believe, 0.005" longer. The military freebore is 0.150" verses 0.090" for a SAAMI standard chamber. So, overall, the NATO chamber is a little more generous, meaning that a SAAMI spec cartridge fired in it will run at a little bit lower peak pressure than it does in a SAAMI chamber, but not much lower.

There is a theoretical possibility that a military specialty cartridge that is short in ogive and long in COL could jam in the shorter commercial freebore, but I've never heard of it happening.

Board member FALPhil, whose brother worked at Aberdeen and could ask some questions there, has a good write-up on the pressure confusion,. But the bottom line is the maximum values both for dimensions and for pressure in the cartridges are actually the same, except for that extra 0.010" of length that SAAMI allows.

[Jim Watson]

Thanks for the history, Unk.
I knew the difference in pressures was illusory, the Army is not a member of SAAMI and were not calling crusher gauge readings CUP.

[Unclenick]

What's funny, IIRC, from FALPhil's article is the guys in the Aberdeen lab actually were using CUP, but the guys editing the tech manuals were the ones changing it. Of course, if you go back far enough, everyone, including SAAMI, was calling copper crusher output psi. I don't know exactly when the CUP language shift occurred, maybe in teh 1960's, but the CIP never did change, either. Like the Army, they used actual pressure units. You just had to know whether they were measured by copper crusher or by a piezo transducer.

[Jim Watson]

If the .308 really was 62,000 psi and the 7.62 50,000 on the same scale, why wasn't there a large difference in velocity? A 24% increase in pressure ought to give 12% more velocity according to the old G&A rule of thumb, or 10% according to an early Vihtavuori booklet.


Anybody know the Real Scoop on the Spanish Mauser conversions?
At one time we thought they were meant for the mild 7.62 CETME variant, but then we were told that they were for 7.62 NATO... but should not be shot with the powerful .308 Win (see above.)

I think they were meant for the NATO load but were not intended to be shot a lot. Border guards and line of communication troops, say.

[Unclenick]

Chambered for the 7.62 NATO, but intended for drilling and cleaning practice, maybe? Could be.