NRA Article Says 308 Ammo's Unsafe in 7.62 Chambers
- Thread starter Bart B.
- Start date
"Personally, I think the whole thing is a tempest in a teapot. Possible, I suppose, but people have been shooting commercial .308 ammo in military firearms for almost 70 years now, and there hasn't been any significant number of problems reported during that time, so, I suspect the future won't be much different."
Now here we agree 100%.
Now here we agree 100%.
The real problem is the article includes apples-to-oranges comparisons. Do the CIP and NATO use the same pressure standard? Yes and no. Both NATO and the CIP use 4150 bar or 415 MegaPascals (60,191 psi) as the maximum average peak pressure number. However, the CIP measures using a piezoelectric transducer element that samples the pressure through a hole drilled in the case 25 mm (.9843 inches) from the face of the case head, while the NATO EPVAT method puts a hole in front of the case mouth in the chamber and measures with a piezoelectric transducer there, where as much as a 2,000 psi drop, as compared to the case hole location can occur due to the pressurized gas trying to keep up with the accelerating bullet. So it seems likely that, unless NATO and the CIP membership share reference ammunition, NATO will tend to load with a slightly warmer absolute limit when measured as the CIP does it. Meanwhile, back in the U.S.A., we have the conformal transducer that measures pressure over top of the brass, so the transducer isn't exposed directly to it as the other two devices try to do it. This leads to some significant known differences in peak pressure readings. For example, NATO SS109, copied by M855, will read about 58,200 psi on a conformal transducer, rather than 60,191 psi.
As to where the difference between what was ultimately adopted as M80 and what became 308 Winchester, that, I suspect, is entirely traceable to later development changes made to increase the number of rounds between failures to feed or to fire. Both seem to have started out at the 52,000 C.U.P. (the military calls it psi by copper crusher) that was introduced via SAAMI by Winchester as 308 Winchester. But owing to the desire to increase feeding and firing reliability, the military started to change the chamber, making it both wider and longer and increasing the freebore. Needless to say, those efforts will drop the peak chamber pressure both by increasing expanded case volume and by allowing a longer period of gas bypass while the bullet goes through the extra freebore. So a 308 Winchester fired in a SAAMI chamber spec pressure gun and one fired in a 7.62 NATO spec chamber is to be expected to peak at a lower pressure anyway, and I suspect the military just went with that as its standard because of the way the numbers came out. Add to this that the military copper crusher is not an exact match to the SAAMI one, and it is easy to see a 2,000 psi/CUP difference creeping into the specification.
Finally, as the brass stretching, anyone who has fired a parent cartridge in an Ackley Improved chamber to achieve initial fire-forming knows the 308 Win brass isn't going to be damaged by fire-forming to the much smaller difference between 308 Win and 7.62 NATO chambers. It just won't matter much. Brass will be worked more in the sizing die, but those firing 5.56 or 223 Rem in Wylde chambers knows the effects on brass life, though real, is not prohibitive.
From the information Clymer used to have on their web site regarding comparative chamber dimensions:
As to where the difference between what was ultimately adopted as M80 and what became 308 Winchester, that, I suspect, is entirely traceable to later development changes made to increase the number of rounds between failures to feed or to fire. Both seem to have started out at the 52,000 C.U.P. (the military calls it psi by copper crusher) that was introduced via SAAMI by Winchester as 308 Winchester. But owing to the desire to increase feeding and firing reliability, the military started to change the chamber, making it both wider and longer and increasing the freebore. Needless to say, those efforts will drop the peak chamber pressure both by increasing expanded case volume and by allowing a longer period of gas bypass while the bullet goes through the extra freebore. So a 308 Winchester fired in a SAAMI chamber spec pressure gun and one fired in a 7.62 NATO spec chamber is to be expected to peak at a lower pressure anyway, and I suspect the military just went with that as its standard because of the way the numbers came out. Add to this that the military copper crusher is not an exact match to the SAAMI one, and it is easy to see a 2,000 psi/CUP difference creeping into the specification.
Finally, as the brass stretching, anyone who has fired a parent cartridge in an Ackley Improved chamber to achieve initial fire-forming knows the 308 Win brass isn't going to be damaged by fire-forming to the much smaller difference between 308 Win and 7.62 NATO chambers. It just won't matter much. Brass will be worked more in the sizing die, but those firing 5.56 or 223 Rem in Wylde chambers knows the effects on brass life, though real, is not prohibitive.
From the information Clymer used to have on their web site regarding comparative chamber dimensions:
Code:
308 Winchester Reamer Dimension in inches and degrees
Type: Rimless
308 M852 308 Palma SAAMI 7.62×51 NATO
A: 0.4370 A: 0.4370 A: 0.4370 A: 0.4370
C: 0.4700 C: 0.4690 C: 0.4700 C: 0.4725
D: 0.4550 D: 0.4550 D: 0.4550 D: 0.4560
E: 0.3430 E: 0.3400 E: 0.3462 E: 0.3460
F: 0.3430 F: 0.3400 F: 0.3442 F: 0.3460
G: 0.3095 G: 0.3085 G: 0.3100 G: 0.3110
H: 0.2990 H: 0.2970 H: 0.2990 H: 0.2990
K: 2.0200 K: 2.0200 K: 2.0250 K: 2.0250
L: 1.3540 L: 1.3540 L: 1.3540 L: 1.3560
M: 0.3120 M: 0.3090 M: 0.3210 M: 0.3200
N: 0.0750 N: 0.0750 N: 0.0900 N: 0.1500
O: 0.2000 O: 0.2000 O: 0.2000 O: 0.2000
Q:20° Q:20° Q:20° Q:20°
R: 1°30' R: 1°30' R: 1°45' R: 2°30'
A Shank, C Base Diameter, D Shoulder Diameter, E Neck-1, F Neck-2/Case Mouth
G Freebore Diameter, H Pilot Diameter, K Min. Chamber Length/Base-to-Case Mouth
L Base-to-Shoulder, M Neck Length, N Freebore Length, O Rim/Belt Thickness,
Q Shoulder Angle, R ThroatMy understanding of the difference between the two has to do with pressure at the gas port on rifles like the M14 being too high when fired with 308 commercial ammo due to slower powders being used for commercial loads. A few thousandths of an inch in base to shoulder length shouldn't be an issue, I have seen lots of ammo over the years that was loaded very short so that it could fit into a minimum-dimensons chamber and it worked fine.
Why would slower powders be used in commercial 308 Winchester cartridges for bullets in the 145 to 180 grain range the 7.62 NATO cartridges have been loaded to for M14 rifles?
Same thing for 30-06 and Caliber 30 M1 cartridges.
Aren't all commercial rifle cartridges sized to function in minimum SAAMI spec chambers?
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I have shot a lot of GI 7.62 in commercial 308 rifles. I have also shot a lot of commercial 308 Win in Springfield M1a. Also handloads of both GI & Commercial brass. Never herd of this till lately. It’s about same crap as the 5.56/ 223 issue that has come up in recent years. 50yrs ago you herd nothing about it. The people making a big deal out of this stuff beat around the bush explaining it like it’s a secret. The secret is they are making a big deal over an “if”.
I never had the occasion to fire 308 in M14, but had a buddy that shot M14 on State Team at Perry. He shot commercial, handloads and GI with no explosions.
I never had the occasion to fire 308 in M14, but had a buddy that shot M14 on State Team at Perry. He shot commercial, handloads and GI with no explosions.
My point exactly, all commercial ammo is loaded short so it works in any gun.
So a 308 chamber being a couple thousandths shorter than 7.62X51 will have no impact.
I thought it was the M1A. Same reason why you load fast powders like 748 for the 7.62 versus 4064 for the 30-06. But I could be wrong.
Because military ammo is loaded to a spec, X velocity at the muzzle with Y SD of velocitties. Commercial ammo is not, and is generally loaded to as fast as it will go.
I don't know about mistranslation, I would call it a mis-understanding.
The gas systems of the M1 Garand and the M14 (M1A) are not identical. The gas piston system used on the M14 is described as "self regulating" meaning that excess port pressure is vented off as the piston moves and clears the vent holes, so a constant amount of force is delivered to the op rod. The original M1 Garand system does not do this and so excess port pressure is transmitted to the op rod and that can cause damage (bent rod).
I understand there is an aftermarket "vented" gas plug that can be installed in a Garand to allow shooting commercial .30-06 without risking damage to the rifle. I don't have any personal experience with this, so I can't verify it's effectiveness.
Question
Why would slower powders be used in commercial 308 Winchester cartridges for bullets in the 145 to 180 grain range the 7.62 NATO cartridges have been loaded to for M14 rifles?
Answer
Because military ammo is loaded to a spec, X velocity at the muzzle with Y SD of velocitties. Commercial ammo is not, and is generally loaded to as fast as it will go.
Facts
Military rifle ammo is loaded to a velocity spec +/- X fps at 26 yards, a psi chamber spec and accuracy spec downrange of some mean radius spec across many dozens of shots.
Commercial ammo is not loaded to attain fastest velocity possible; not a good idea if best accuracy is important. Never heard of this concept before now. Each has it's own pressure, velocity and accuracy specs, not all available to customers.
Comment
Same reason why you load fast powders like 748 for the 7.62 versus 4064 for the 30-06. But I could be wrong.
Reality
Ball powders at any velocity were never popular for best accuracy in both cartridges. 4064 was best in both with 165 to 185 grain bullets.
Why would slower powders be used in commercial 308 Winchester cartridges for bullets in the 145 to 180 grain range the 7.62 NATO cartridges have been loaded to for M14 rifles?
Answer
Because military ammo is loaded to a spec, X velocity at the muzzle with Y SD of velocitties. Commercial ammo is not, and is generally loaded to as fast as it will go.
Facts
Military rifle ammo is loaded to a velocity spec +/- X fps at 26 yards, a psi chamber spec and accuracy spec downrange of some mean radius spec across many dozens of shots.
Commercial ammo is not loaded to attain fastest velocity possible; not a good idea if best accuracy is important. Never heard of this concept before now. Each has it's own pressure, velocity and accuracy specs, not all available to customers.
Comment
Same reason why you load fast powders like 748 for the 7.62 versus 4064 for the 30-06. But I could be wrong.
Reality
Ball powders at any velocity were never popular for best accuracy in both cartridges. 4064 was best in both with 165 to 185 grain bullets.
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For 7.62 NATO there is a gas port pressure window that has to be met. From the old MIL-C-46931F for M80 Ball ammunition (this standard is from when the military and NATO EPVAT method were both carried out by copper slug crushing):
But note the narrow temperature range for that spec. The same ammo had to pass firing at 125°F, where the +2000 number would grow, and at -65°F, where the -2000 number would get smaller. So the guns tolerate a pretty wide range. And while a fast or a slow powder makes quite a big difference in muzzle pressure (which the Garand gas port is near), when the peak pressure matches, the difference to the mid-barrel gas port point on the M14 (13.818 inches from the breech face) represents a smaller difference. Fiddling QuickLOAD around to give the gas port result, in normal weather conditions, if an IMR 4895 load behind the 173 grain M1 Type bullet that makes the average pressure of 12500 psi is replaced with a Reloader 17 load that stuffed to the same peak pressure, still only sees about 1100 psi increase at the gas port. If you go still slower, with 4350, you basically can't get enough in the case to exceed the 4895 gas port pressure (I used 110% compressed as that limit). And until you go to Reloader 10X loaded to the same peak pressure, you can't get the port pressure below spec, either. The M14 gas system is quite tolerant of a range of propellants.
On top of that, you never would load all those powders to the same peak because of the military velocity window requirement which is ±30 fps average. So the slow powders get loaded to a lower peak, which helps regulate the port pressure. Working the same problem with a 147-grain bullet brings about similar results. The bottom line is that you have to go to some extreme trouble to violate the port pressure limit on either side, and that's why commercial loads don't cause problems in the M14-based rifles.
3.8 Port pressure. The port pressure measurement can be performed by either the copper-crush cylinder or EPVAT test method. The average port pressure of the sample cartridges when conditioned for not less than 2 hours at 68° to 72°F and fired at that temperature shall be as noted in the applicable sub-paragraphs :
3.8.1 Measurement by copper-crush cylinder test method. The average port pressure of the sample cartridges shall be 12,500 psi ± 2,000 psi.
3.8.1 Measurement by copper-crush cylinder test method. The average port pressure of the sample cartridges shall be 12,500 psi ± 2,000 psi.
But note the narrow temperature range for that spec. The same ammo had to pass firing at 125°F, where the +2000 number would grow, and at -65°F, where the -2000 number would get smaller. So the guns tolerate a pretty wide range. And while a fast or a slow powder makes quite a big difference in muzzle pressure (which the Garand gas port is near), when the peak pressure matches, the difference to the mid-barrel gas port point on the M14 (13.818 inches from the breech face) represents a smaller difference. Fiddling QuickLOAD around to give the gas port result, in normal weather conditions, if an IMR 4895 load behind the 173 grain M1 Type bullet that makes the average pressure of 12500 psi is replaced with a Reloader 17 load that stuffed to the same peak pressure, still only sees about 1100 psi increase at the gas port. If you go still slower, with 4350, you basically can't get enough in the case to exceed the 4895 gas port pressure (I used 110% compressed as that limit). And until you go to Reloader 10X loaded to the same peak pressure, you can't get the port pressure below spec, either. The M14 gas system is quite tolerant of a range of propellants.
On top of that, you never would load all those powders to the same peak because of the military velocity window requirement which is ±30 fps average. So the slow powders get loaded to a lower peak, which helps regulate the port pressure. Working the same problem with a 147-grain bullet brings about similar results. The bottom line is that you have to go to some extreme trouble to violate the port pressure limit on either side, and that's why commercial loads don't cause problems in the M14-based rifles.
When I started shooting high power rifle matches in 1965, there were some people who were afraid to be next to anyone using anyone using a 7.62 NATO Garand. They were convinced the ammo had higher pressures than 30-06 Garands because the ammo made a different sound when fired.
Yes, different because gas port pressure was less. 7.62 versions needed a larger diameter gas port. The 7.62 sound wave was shaped different than 30-06 ones
Yes, different because gas port pressure was less. 7.62 versions needed a larger diameter gas port. The 7.62 sound wave was shaped different than 30-06 ones
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Spanish Mauser?
I do believe that Century has been selling the old 1916 small ring Spanish Mauser for decades now.
These rifles were originally 7mm Mauser caliber, and were rechambered to 7.62 NATO by the Spanish.
I owned one for many years, I shot 7.62 milsurp and .308 Win interchangeably in that old Mauser for a long time. Mostly milsurp "blasting" ammo, have no idea how much .308 I put through it.
Apparently according to all the online experts I risked life and esp. limb with every pull of the trigger.
I do not recommend the above, just stating my experience. Upon further research learned that the debate over these Mausers has been going strong since they were first sold as surplus.
I do remember that little Mauser kicked like a mule with either flavor of ammo. I think I paid 69 bucks for it.
I do believe that Century has been selling the old 1916 small ring Spanish Mauser for decades now.
These rifles were originally 7mm Mauser caliber, and were rechambered to 7.62 NATO by the Spanish.
I owned one for many years, I shot 7.62 milsurp and .308 Win interchangeably in that old Mauser for a long time. Mostly milsurp "blasting" ammo, have no idea how much .308 I put through it.
Apparently according to all the online experts I risked life and esp. limb with every pull of the trigger.
I do not recommend the above, just stating my experience. Upon further research learned that the debate over these Mausers has been going strong since they were first sold as surplus.
I do remember that little Mauser kicked like a mule with either flavor of ammo. I think I paid 69 bucks for it.
The debate is due to the fact that they were not rechambered to 7.62 NATO. They were rechamberd to the Spanish 7.62mm round (developed with the original CETME rifle) which is dimensionally the same as the 7.62 NATO but is lower pressure.
When sold for surplus they were sold to the consumers as 7.62 NATO and some people got concerned about the "higher pressure" NATO round in the small ring Mauser causing lug setback, or even complete failure.
It doesn't seem to have happened to any significant number of rifles, so I can't say its a problem, or not, but the argument rages on...
What factual evidence are you basing your opinion on?
I would need to know what such ammo's port pressures are before having an opinion. If there's more area under the pressure curves but port pressures are safe, that will cause bullets to leave faster.
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For practical purposes, at the range in the desert, shooting whatever, to me this seems to be so blown out of proportion to any actual issues that I have encountered.
I've been firing new, commercial 308 of various US and foreign manufacture, new Lake City 7.62 and new mil-surp 7.62, foreign and domestic, in my M1A Standard for a couple of decades: no issues, no problems, no missing fingers, eyes or nose, no hang fires or hangnails, no blasted out rifle parts, ever.
Mostly I fire my handloads which consist of two full 30 cal ammo cans that hold about 700 rounds each of well used, mixed head stamp brass, match and non-match, Winchester, Federal, Remington, Nosler, Lake City, mil-surp, and whatever else is in there, loaded with 168 gr match bullets by Sierra, Hornady, Nosler and bulk packs of unknown manufacture, pulled and new, loaded with 42 gr of 4064 using various primers: CCI #34, CCI large rifle, Winchester large rifle and Remington large rifle, as available when I run out of components and need to stock up again.
With the potpourri of ammo in those two ammo cans, I can rings gongs at 300 yards all day long until my tired, old, crusty eyes and my well worn shoulder give out.
The only brass sorting I do after tumbling is: cracked cases and cases with worn out primer holes go in the trash. All cases get trimmed to 2", all bullets are 168 gr match, all cases hold 42 gr of 4064 and OAL is always 2.81". All rounds are loaded on a Bonanza press using RCBS, small base 308 dies.
I'm an old Navy man, which is where I fired M-14's. I am not an NRA certified anything nor am I an engineer. I have been shooting for 40 years and handloading for 30 years.
I just don't see what all the fuss is about.
I've been firing new, commercial 308 of various US and foreign manufacture, new Lake City 7.62 and new mil-surp 7.62, foreign and domestic, in my M1A Standard for a couple of decades: no issues, no problems, no missing fingers, eyes or nose, no hang fires or hangnails, no blasted out rifle parts, ever.
Mostly I fire my handloads which consist of two full 30 cal ammo cans that hold about 700 rounds each of well used, mixed head stamp brass, match and non-match, Winchester, Federal, Remington, Nosler, Lake City, mil-surp, and whatever else is in there, loaded with 168 gr match bullets by Sierra, Hornady, Nosler and bulk packs of unknown manufacture, pulled and new, loaded with 42 gr of 4064 using various primers: CCI #34, CCI large rifle, Winchester large rifle and Remington large rifle, as available when I run out of components and need to stock up again.
With the potpourri of ammo in those two ammo cans, I can rings gongs at 300 yards all day long until my tired, old, crusty eyes and my well worn shoulder give out.
The only brass sorting I do after tumbling is: cracked cases and cases with worn out primer holes go in the trash. All cases get trimmed to 2", all bullets are 168 gr match, all cases hold 42 gr of 4064 and OAL is always 2.81". All rounds are loaded on a Bonanza press using RCBS, small base 308 dies.
I'm an old Navy man, which is where I fired M-14's. I am not an NRA certified anything nor am I an engineer. I have been shooting for 40 years and handloading for 30 years.
I just don't see what all the fuss is about.
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