Why slightly different civilian versions of 7.62 and 5.56 NATO?

[DMK]

Here's a question that I've been curious about for some time: Why did Winchester and Remington change the specs of 7.62 and 5.56 NATO to make make civilian versions(.308 Win and .223 Rem respectively)? If the round was already developed and working, why change the specs slightly for civilian use? It wasn't done for 30.06, or 45-70 which were both military rounds that gained much popularity with civilian shooters.

 

[Jacobus Rex]

Ammunition made for the US market follows SAAMI specs that will be a little different than ammo made in other countries or ammo made to military standards. In the case of 5.56, the military ammo is made to NATO specs that are slightly different than US SAAMI specs.

 

[DWARREN123]

The ammo is different because it is used for hunting/plinking not combat.

 

[combatpreacher]

Military must function in "Machineguns" and potetialy dirty weapons...thicker brass and "looser" chambers ensure reliability.

Thicker brass means less room for powder and more pressure if you try to duplicate some "civilian" loads.

I pitted the boltface on a nice Remington Model 7 in 223 this way...oops!

 

[Grump]

If the round was already developed and working, why change the specs slightly for civilian use?

Premise of the question is demonstrably false.

Winchester rushed the .308 to market BEFORE 7.62 NATO's specs were finalized. SAAMI got frozen in time at a point earlier than the NATO specs. As I have repeatedly posted elsewhere, a lot of hot air is blown about, and drawings are easily found, showing the differences of about .003 or .006 [details escape me right now] between the chambers of the two rounds, but no one has been able or willing to point me to any drawings of both rounds' CARTRIDGE DIMENSIONS. If the cartridge dimensions are the same, then we know for certain what min/max tolerances and gaps are....for rounds in the chamber...

I'm not as certain on the .223/5.56mm. The 55-gr M193 was never a NATO round, AFIK. That began when the M16 was finally built right with decent ammo, IME, in--what??--1985, after about 20 years of service. The big difference between SAAMI .223 chambers and M193 chambers is the throat--M193 ammo jams into the leade/lands and spike pressures. I've never been able to find data on the M855 NATO ammo to determine if a similar hazard exists... I'm sure Remington also put theirs out to market before the military was done tweaking with it. Being thought of as a modified .222 Magnum, the .223 Remington was apparently designed for bullets up to 52 grains, of typical expanding varmint construction, and with shorter ogives.

 

[Bartholomew Roberts]

Going from memory here so large portions of this may be erroneous; but Remington developed the .223 Rem as part of Army trials. They had standardized with SAAMI and released the product to the civilian market when the Army complained that the 55gr load they had chosen did not reliably penetrate a steel helmet at the required distance (500m?). So Remington tweaked it to be a little hotter and give a little more margin for error.

 

[DMK]

OK, so it seems then that for both these rounds, the civilian versions were finalized before the military rounds were finalized. That explains the slight differences.

It just seemed strange to me. You don't see two different chamber specs for 30-06, or 45-70 or 9mm or 45ACP. All those were military rounds. It didn't make any sense to me why someone would "reinvent the wheel" to sell the ammo in the civilian market. Business don't usually waste money like that without a good reason.

 

[AJ Dual]

The main reason that those older rounds don't have disparities between SAMMI and military is that SAMMI didn't exist back then.

The other reason for the differences (in more current calibers) is that SAMMI and NATO spec aren't even always measuring the same things.

They are very close, but in general SAMMI .223 Remington chambers have tighter headspace, and much less freebore before the rifling is engaged. Putting 5.56mm military ammunition in a .223 chamber can cause high pressure. SAMMI chambers are designed for sporting arms where accuracy is generaly more important than absolute reliability.

(Although some commercial semi-autos marked as ".223" may actualy have NATO reamed chambers to increase reliablity, and because .223 in a 5.56 chamber is the "safe" combination.)

If a SAMMI-chambered sporting arm fails, you lose the deer. If a military chambered arm fails, you might lose your life. Although in many calibers SAMMI and military spec. are often in agreement, or at least have lots of overlap in the selection of loadings availible.

A NATO chamber has looser headspace, and more freebore before the rifling starts to aid in reliability, and the firing of differing cartrdige lengths like the .223 tracer.

As a general rule, you can shoot .223 in a 5.56 NATO chamber, but 5.56 NATO should be avoided in a .223 chamber. The 5.56 NATO spec is approximately 10,000 cup higher in pressure than the SAMMI spec for .223. The Tighter chamber, and shorter freebore before rifling begins might drive the pressure difference even higher.

I don't think there's an "offical" SAMMI warnig for .308 and 7.62 NATO though. There the concern is often the opposite, that "hot" commercial .308 made for bolt-action hunting rifles should be avoided in Military 7.62 chambers. Perhaps that's because SAMMI normally concerns itself with commercial arms cut with commercial chambers.

 

[rockstar.esq]

Interesting thread, thanks to all that posted. I wonder if shooters feel that the NATO naming conventions are more straightforward than commercial monikers? Of course NATO has the advantage of having far fewer cartridgest to deal with...

 

[Mannlicher]

I know all individual rifles can be different, but in my experience, I have used NATO spec ammo in my sporting rifles, and SAAMI spec ammo in my military spec rifles for years, with no ill effects.

 

[Jim K]

I, too, have used both military and civilian rounds interchangeably in both military and civilian rifles with no problems. IMHO, the difference is theoretical, and of no real significance.

Some folks seem to think loading a 7.62 NATO round in a .308 Winchester chamber, or vice versa, will cause the rifle to blow up in a mushroom cloud and wipe out all life on earth. Doesn't happen.

I will note that .308 commercial ammo has a higher max pressure than 7.62x51 NATO and I don't really recommend either for those older rifles (93-96 Mausers) originally chambered for medium pressure rounds like the 7x57 Mauser.

Jim