7.62x51 vs .308win AND 5.56x45 vs .223rem

[pandemic]

I know this topic has been covered a lot. I'm just a bit confused about it. I found and read the following thread:
http://forum.pafoa.org/rifles-42/457...s-7-62x51.html

It says (more or less) that it IS safe to shoot .308 Win in rifles chambered for 7.62x51. However, is it safe to fire 7.62x51 in rifles chambered for .308 win?


Same for the 5.56x45 vs .223 rem debate.

Is it safe to fire 5.56x45 in a rifle chambered for .223 rem?

Is it safe to fire .223 rem in a rifle chambered for 5.56x45?


I've read a lot that you should check head spacing. How would I go about doing that? I have a feeling the answer is going to be "take it to a gun smith."

Thanks very much for the info.

[ScaredOnce]

Pressure .

[pandemic]

Pressure .

That's what I read on the other thread but I don't understand the different pressures exactly or if they matter.

PS: Sorry, mod, for posting in the wrong section.

I Heard that rifles chambered for 7.62x51 should not shoot .308 Win. Confirmed this by reviewing SAAMI spec - the allowable pressures for .308 are 62,000 psi & the allowable pressures for 7.62x51 are 50,000 psi. The opposite of .223 vs. 5.56x45. So, when shooting FALs, M1As, AR-10s - should .308 Win not be used?

Sigh.

You are comparing apples and kumquats. SAAMI specs are in Piezo-measured psi, military, in crusher-measured CUP (Copper Units of Pressure). There is no meaningful nor practical way to correlate the two measurement systems.

The difference in cartridges, whether dimension or performance, are negligible, if any. The only consideration is whether your rifle has a "long" military chamber, e.g., the USGI military chamber. Unless you have one of the 50 or so M14s in private hands, or one of the few thousand 7.62-MM "Navy" Garands, you'll not see a USGI 7.62-MM military chamber in a US-made rifle.

Check the headspace; if it falls within .308 Winchester specifications, you're good to go. M1As, Fulton ARmory M14s and Titan UPRs, other AR-type .308s are all chambered for .308 Winchester dimensions.

I have two "7.62-MM" marked rifles. One, an Ishapore 2A, has a "long" military chamber (the bolt closes on .308 NO-GO, though not on FIELD). I will use only cartridges with military brass in order to stand the gaff. My Sterling-converted 7.62-MM No 4 Mk 1*, on the other hand, is .308-Winchester headspaced.

Note that we have never found a 7.62-MM (that's the US Army way of saying "7.62x51mm 'NATO'") cartridge that did not fall within .308 Winchester SAAMI dimensions, so the .308 chambers found in Fulton Armory rifles and M1As and the like accept 7.62-MM cartridges just fine.

One of my correspondents has written a marvelous FAQ article which will be up on the Fulton Armory FAQ Page in due course.

Watch out for those apples and kumquats .

Regards,

Walt

[Biggfoot44]

The other issue is with certain surplus rifles, in recent decades particularly Spanish surplus FR6 IIRC, with was a '93 pattern Mauser converted to "7.62", and early production CTMEs . At the time Spain loaded a dimentional.similar ctg, but to slightly lower pressures.
Importers have proofed the Mausers, but most authorities consider full .308/ NATO pressures beyond the design capability of '93s .
Late production CTMEs were made for regular NATO ammo.

[762xIan]

Scroll about 1/2 way down this page, It is a Q and A section, he lists some of the technical info associated with the differences between the cartridges and what to look out for.

http://www.frfrogspad.com/miscelld.htm#5.56%20mm%20NATO

However, is it safe to fire 7.62x51 in rifles chambered for .308 win?

Yes....but don't expect great accuracy with the milsurp ammo.

Is it safe to fire 5.56x45 in a rifle chambered for .223 rem?

This is where the problem lies....the milsurp 5.56 is usually hotter than commercial .223, and this is where the headspace issue comes into play as well.

Is it safe to fire .223 rem in a rifle chambered for 5.56x45?

Yes, but again don't expect great accuracy.

One of the latest and greatest offerings is the "Wylde" chambering. Wylde is supposed to be an in-between SAAMI and MIL-SPEC so it allows you to use either/or and give you almost the accuracy of a real SAAMI when using the good .223 ammo but also allow you to use cheap surplus ball ammo safely.

I've read a lot that you should check head spacing. How would I go about doing that? I have a feeling the answer is going to be "take it to a gun smith."

To check a rifles headspace, you need specific gauges for each caliber, a "go", a "no-go" and a "field". Gauges can be pretty expensive, usually about $30 each.

Unless you are re-barreling a rifle, buying a lot of old or surplus rifles and want to check them prior to purchase, or into gunsmithing you really don't need them.

Stick to ammo your rifles are chambered for, know what to look for as far as problem areas with your fired cases, such as constant split necks, blown or separated cases, or very poor accuracy with all types of ammo. These are the types of problems associated with headspace issues. Which pretty much means you need a new barrel and a gunsmith.