7.62 NATO; Long Range Match Ammo History

[Bart B.]

Well written, good information on the triumphs and pitfalls of this cartridge (and its commercial version, the .308 Winchester, when applicable) in the M14 and M1 service rifles:

http://riflemansjournal.blogspot.com...nge-match.html

[rocket305]

Thanks for that very informative article. I was a member of Army and National Guard teams from 1967-2006, and never saw that much excellent info in one place. I read the whole article, and it brought back many good memories. Thanks again, and keep up the good work. L L Walraven

[kraigwy]

Indeed a great article, I was a Guard shooter until I retired in '92 but didn't "keep up" after I retired.

This article brings me up to date.

[pbcaster45]

I hope German starts writing again soon, his articles are just awesome.

[Rainbow Demon]

A great site, I contributed a few links years ago and I'm happy to see how the site has grown.

I've tried to warn owners of the older conversions to 7.62 that some of the long range match ammo of today is far more potent than the ammo these rifles were intended to use (M80 Ball or similar with 48,000 CUP ), but seldom with any success. The NRA UK has also had difficulty in convincing shooters there that they may damage their rifles with some modern long range ammo.

PS
Some of the converted rifles were only proofed at 58,000 CUP when new, and some long range loads are in the neighborhood of 59,000 CUP.
The Birmingham Proof Authority and NRA UK have mandated re proofing of 7.62 NATO conversion rifles if used in competition, and instituted inspections of bore size and chamber neck dimensions which now must meet a minimum specification.

[Bart B.]

Rainbow Demon, you are so right about some long range loads being a bit much for some rifles. In the USA arsenals specs, average peak pressure for the 7.62 NATO's 50,000 CUP. But the military teams oft times went beyond that.

That articles reference to replacing M80 ammo's 147-gr. ball bullet with a Sierra 168 ended up with a round with almost MIL SPEC proof load pressures. The proof load was a 172-gr. match bullet atop 41 grains of IMR4475 stick powder; the powder used in M80 ammo that was the favorite for swapping bullets on. It produced 65,000 CUP and with the 168, about the same. But the M14's and M1's shooting it had no problems as their receivers are robust enough to easily handle it. And with well fit operating rods, they stayed straight. I've shot that "proof" load in matches pulling bullets from those M80 lots and replacing them with 172's pulled to make the load shown below.

That US Air Force load with 44 grains of IMR4320 under a Sierra 190 in a new primed M118 match ammo case was the most accurate load for long range ever used in M1 Garands rebarreled to 7 .62 NATO. I've known its US Air Force Rifle Team developer since 1965 and he shared it with the USN Rifle Team. In a conversation about that load with a ballistics engineer at Lake City Army Ammo Plant back in the '70's, he said that load was no doubt over 60,000 CUP.

[Jimro]

I think Rainbow Demon is referring to converted Lee Enfields from 303 Brit to 7.62 Nato and used in fullbore competition.

Any modern front locking bolt action rifle should have no problem with modern long range ammo, although if you have a gas system involved sometimes it needs tweeking, such as drilling a relief hole in the gas port for M14s or M1As for shooting that 190gr load (still a legal modification for competition today).

Jimro

[Bart B.]

Jimro, I knew he was referring to the converted .303's, but 'twas probably good for others reading this threa that you mentioned that.

None of the M1 or M14 rifles had relief ports when I was shooting such heavy loads. I don't think that such modied gas system were even thought of back in the '60's and '70's. The extra loud ring of the metal parts being smacked extra hard by moving parts told the shooter a heavy load was just fired.

[Rainbow Demon]

I was also speaking of the Chilean 1895 and Spanish 93 and 95 actions.
While these are plenty safe enough with M80 Ball if rebarreled properly and in good condition, some Chilean rifles were instead rebored and a chamber insert soldered into a reamed out chamber shoulder to take up the slack between the 7mm 57mm chamber and the 51mm chamber of the 7.62 NATO.

While some of the Spanish rifles have digested regular M80 Ball and the more common .308 hunting loads with no problems, others exhibit lug recess set back, and there have been a few blow ups, though defective ammo is the most likely cause.

Most 98 actions have a much greater safety margin. Some of these have had problems with set back when extra heavy loads are used.
While machining is pretty good on any license built Mauser (with the exception of a small run of FN Mausers that suffered cracked lugs due to insifficient radius cuts),Metalurgy and thickness of the carburized layer runs the gamit.

The problem isn't so much with the rifles, but rather the poor quality of a lot of NATO surplus ammo.

19th century German proof testing took degradation of propellents into consideration. The Special powder used for proof testing was formulated to give the aprox pressure of a propellent damaged by poor storage in tropical climes.
Powder charge weight was the same as the regular powder but pressure about 20-25% higher.
The Gew 88, the Model 91, and Model 93 were proofed at 58,000 CUP.
The 98 rifles were proofed at higher presures, IIRC around 75-78K CUP.

The 1895 Winchester operated fine with WW1 era .30-06 ammo at 48,000 CUP but often suffered lug set back with M1 Ball at 50,000+ CUP.

PS
The greater the operating pressure of a particular load the greater the pressure increase one may expect from any degradation of the propellent.

[Jimro]

Bart B.

I guess when Uncle Sam is paying for rifles and parts (and winning scores) then part longevity is a secondary concern. I think it was the Air Force that tried the relief hole modification in the gas port of the M14, but I don't know if it was just a few rifles or if it was a standard modification for their service rifle team or a "one off" they tried. Somehow that modification is still legal in the books, but my memory isn't as reliable as Google anymore.

Rainbow Demon,

Good point about those small ring Mauser actions. I had a K.Kale Large Ring Small Shank Turk case hardened (the gunsmith I had do the metal work had it sent to a machine shop that would work on receivers) simply because those Turks had very tough steel, but almost universally suffered from poor heat treatment. That ended up a very nice 9.3x62 that I have full confidence in. With the small shank diameter I didn't trust it with a magnum brass diameter.

On the other hand, Kimber imported some Swede actions and proofed them for 308 loads and sold them on the American market. I haven't heard any horror stories yet about those rifles, but I have seen photos of Swedes that went "kaboom" due to hot loads.

Jimro

[Bart B.]

Jimro, none of the USN modified and rebarreled M1 receivers, bolts, op rods or other parts suffered in any way from thousands of rounds of Mexican match or stiff 190 loads at or very close to proof load pressures. Both of the ones I had rebarreled were checked for headspace as a safety thing after about 2000 rounds of 190's and Mexican Match and another 3000 rounds of M118 match ammo. Headspace didn't open up at all and no op rod problems. Some of the USN receivers were magnafluxed after going through 3 barrels firing such loads in each; no cracks at all. That's one things that'd amazed me about Garands.

[Rainbow Demon]

Hatcher wrote of a Garand put to the test with specialy assembled loads of 125,000 CUP. Thats far above the cold flow and rupture point of standard cartridge cases, the test cartridges used specially made cases.
The Garand digested a lot of these rounds before any damaged showed, and that was a broken lug on the bolt, not damage to the receiver.
They continued firing with the broken bolt with no mishaps.

There have been custom straightpull rifles built on the Garand receivers and chambered for ungodly hot experimental cartridges. They built some in 60's or earlier, and a few in recent years.