7.62 vs .308

Huntsman said:
Is'nt .308 Win just the commercial name given to the military ctg 7.62?? Afterall, Winchester was the company to manufacture the 7.62 way back when the US Army wanted a new shorter ctg. Maybe people are reading too far into the .308 & 7.62??
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Not quite. Winchester was very anxious to get the .308 Win. out to the public, so anxious that they did not wait for the official announcement of which of the several prototype cartridges being considered at Aberdeen would be officially adopted. Instead they gambled on which one would be chosen, and tooled up to make it. The DoD eventually settled on the T65E4 prototype as the model for the 7.62x51mm, while Winchester had gone with another of the T65 series. Hence, the rounds are slightly different.

The fact of the matter is that .308 Win is loaded to a lower pressure than 7.62, and the military rifles have a long throat that will lower pressures further, so I wouldn't hesitate for a second to shoot .308 in a 7.62 rifle. Brass is a very ductile material, and will stretch to fill many, many thousandths of excess headspace. The .003" difference in the two chambers doesn't amount to a hill of beans.
 
The fact of the matter is that .308 Win is loaded to a lower pressure than 7.62, and the military rifles have a long throat that will lower pressures further, so I wouldn't hesitate for a second to shoot .308 in a 7.62 rifle. Brass is a very ductile material, and will stretch to fill many, many thousandths of excess headspace. The .003" difference in the two chambers doesn't amount to a hill of beans.[/QUOTE]

Thank you, I've been thinking the same thing. I asked the origional thread question and no one has proved that it makes any difference. For the number of 7.62mm guns out there (M-14, AR180, etc.), I've not found one real instance of any catastrophic failure due to using 7.62 vs .308. Alot of experts with tales of doomsday, but no proof.
 
Katana said:
I believe you have them backwards.

7.62 Nato has a maximum pressure of 50,000 psi
.308 Winchester has a maximum pressure of 62,000 psi...
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Oops, so I do.

Googling around, it turns out there is a lot of contention about this. Lots of people warn that they are not compatible. And the truth is, I once did watch a guy pull the front of a .308 case out of a L1A1 that had seen the case head separate on firing (no one was hurt, and the rifle suffered no damage).

It is useful to know that SAAMI does not counsel against using 7.62x51 ammo in .308 rifles (they do say not to use 5.56x45 in .223 rifles) http://www.saami.org/Unsafe_Combinations.cfm . It is not in SAAMI's mandate to comment on .308 in 7.62 rifles.

I must say that I am baffled by the huge difference in published pressures for the two cartridges. I think the actual pressures must be much closer in practice. There is no reason to think military guns aren't (or can't be) as strong as commercial ones, so why the difference? Gas port pressures, maybe?
 
To be absolutely safe, Tie the rifle to an oak sapling in the dark of the moon strip naked, paint druidic symbols with woad on your body, and walk around it widdershins three times while shaking a bag of .308 brass and reciting "Oh Canada" backwards. This should remove the curse.:D

Or you could just have the headspace checked and shoot the thing.;)
 
One reason the pressure numbers are different is because there are different systems of measuring pressure. If you are looking at numbers, see if the terms cup or psi are used. They aren't the same. Pressures may be determined with a hole in the case and barrel, connecting with a piston (for cup), or with a strain gauge. It also depends on where on the barrel the pressure is read. Half way along the cartridge case will give different numbers than in the throat area.
You cannot make a meaningful comparison of pressure numbers unless they were obtained the same way.
 
These were taken off Wikipedia:
I've highlighted the differnences in bold. I was told that the major between the two is that 7.62 Nato has thicked brass therefor not able to hold as much powder and it is .003 shorted too...

7.62x51 Nato
Parent case .300 Savage
Case type Rimless, Bottleneck
Bullet diameter 7.82 mm (0.308 in)
Neck diameter 8.58 mm (0.338 in)
Shoulder diameter 11.35 mm (0.447 in)
Base diameter 11.84 mm (0.466 in)
Rim diameter 11.94 mm (0.470 in)
Rim thickness 1.27 mm (0.050 in)
Case length 51.05 mm (2.010 in)
Overall length 69.85 mm (2.750 in)
Rifling twist 1:12"
Primer type Large Rifle
Maximum pressure 344.74 MPa (50,000 psi)

.308 Winchester
Parent case .300 Savage
Case type Rimless, Bottleneck
Bullet diameter 0.308 in (7.8 mm)
Neck diameter 0.343 in (8.7 mm)
Shoulder diameter 0.454 in (11.5 mm)
Base diameter 0.470 in (11.9 mm)
Rim diameter 0.473 in (12.0 mm)
Rim thickness 0.050 in (1.3 mm)
Case length 2.015 in (51.2 mm)
Overall length 2.80 in (71 mm)
Rifling twist 1/12
Primer type Large Rifle
Maximum pressure 62,000 psi (430 MPa)


John Sukey said:
To be absolutely safe, Tie the rifle to an oak sapling in the dark of the moon strip naked, paint druidic symbols with woad on your body, and walk around it widdershins three times while shaking a bag of .308 brass and reciting "Oh Canada" backwards. This should remove the curse.:D

Or you could just have the headspace checked and shoot the thing.;)
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That was too funny!!! :D
 
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John Sukey said:
To be absolutely safe, Tie the rifle to an oak sapling in the dark of the moon strip naked, paint druidic symbols with woad on your body, and walk around it widdershins three times while shaking a bag of .308 brass and reciting "Oh Canada" backwards. This should remove the curse.:D

Or you could just have the headspace checked and shoot the thing.;)
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I see you have heard about my shooting ritual.:dancingbanana:

In all seriousness, I have shot around 500-600 of plain jane 150 grain .308 with my M14 and have never had any problems.
 
Katana said:
These were taken off Wikipedia:
I've highlighted the differnences in bold. I was told that the major between the two is that 7.62 Nato has thicked brass therefor not able to hold as much powder and it is .003 shorted too...

7.62x51 Nato
Parent case .300 Savage
Case type Rimless, Bottleneck
Bullet diameter 7.82 mm (0.308 in)
Neck diameter 8.58 mm (0.338 in)
Shoulder diameter 11.35 mm (0.447 in)
Base diameter 11.84 mm (0.466 in)
Rim diameter 11.94 mm (0.470 in)
Rim thickness 1.27 mm (0.050 in)
Case length 51.05 mm (2.010 in)
Overall length 69.85 mm (2.750 in)
Rifling twist 1:12"
Primer type Large Rifle
Maximum pressure 344.74 MPa (50,000 psi)

.308 Winchester
Parent case .300 Savage
Case type Rimless, Bottleneck
Bullet diameter 0.308 in (7.8 mm)
Neck diameter 0.343 in (8.7 mm)
Shoulder diameter 0.454 in (11.5 mm)
Base diameter 0.470 in (11.9 mm)
Rim diameter 0.473 in (12.0 mm)
Rim thickness 0.050 in (1.3 mm)
Case length 2.015 in (51.2 mm)
Overall length 2.80 in (71 mm)
Rifling twist 1/12
Primer type Large Rifle
Maximum pressure 62,000 psi (430 MPa)




That was too funny!!! :D
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anybody else notice the typo ?- bullet diameter is not 7.8, or 7.82, but 7.62- as for the twist, it varies by gun manufacturer- 1.12, 1/11. and 1/10- my savage and the m14s are 1/12, but the remmy is a 1/10-
 
Wikipedia can be a great source of mis-information at times. I know if I let my .308 cases get out to 2.015" they won't chamber. I also have to go with t-star about barrel twist, my target rifle has a 1:14 and my 40X had a 1:10.
 
Seems to me that most of the stuff on the internet that I have read talks about higher pressures with heavy/non-standard bullet weights. It seems to me that a 147 or 150 grain .308, or a 147 or 150 grain 7.62 should interchange just fine and that it is only a problem when you handload unusual (heavy) bullets. Just my $.02
 
Poparelli said:
That's another thing... around here surplus 7.62 is near impossible to come by short of ordering it by the crate. If you don't want to spend all that money you're pretty much stuck with .308.

Also somebody who's an expert please correct me if I'm wrong, but the way I understand it, if you have correct headspacing for .308 you're good to shoot both, but if you're only good for 7.62 then that's all you can safely use.
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That's my understanding as well.
 
I have one point to add to this discussion.

An M14 or M1A is intended to shoot 7.62 ammo with a bullet weight of 148 grains(I think). Shooting heavier rounds such as 180 grains will "batter" the operating rod/action, and may eventually cause it to fail.

I think that 150 grain 308 ammo will be OK. I suspect that heavier bullets should be avoided, both because they are bad for the action, and because the chamber pressure is likely to be higher.

APG
 
Just stick to light load .308 in 7.62 such as 150grain, dont go up to 180grains or higher. We all use it, I use it, most people use it. No problems. Theres plenty of internet hogwash out there that will tell you otherwise, but its all BS. Just stick to light bullets when using .308 in 7.62. Thats it.
 
I've shot one box of 180grain Winchester Super X (before I ever read anything about avoiding heavier bullets) and a few boxes of 150grain Federal.

No trouble with any of it; but I'm still going to get headspace checked before I go shooting again. All the reading I've done now, despite being basically inconclusive on the issue, has made me a bit paranoid...
 
The facts are glaringly obvious to anyone that knows history-designed for 150 gr

This whole story goes way back to 1936-40 during the development of the M1 garand.

The 06 round used a 150 grain bullet originally and then moved to around a 180 gr pill I believe in either the late twenties or early thirties, and at that time it was being used in the 1903 bolt action rifle.

When the Garand came along they found out quite quickly that the operating rod was battered as was the bolt with the 180 grain bullet so they moved quickly back to the 150 grain bullet for all of World War two and beyond.

The 180 grain bullet required a different powder that proved to batter the Garands operating rod and bolt to the point of failures. But when they designed the 30/06 round in the late thirties tailoring it to the M1 Garands port pressure requirements it worked well --this was a 150 grain bullet and IMR 4895 powder.

Which stands for Improved military Powder number 4895.

So after WW2 they decided that they wanted a full auto availability and along came the improved garand design the M1 and yes lo and behold the same basic operating system "improved yes" but basically the same.

Required the same tailoring of the new 7.62 NATO cartridge for chamber pressure and more importantly ---port pressure of the operating system.

This again was found to be with a 150 grain bullet and a tailored powder. To this day it is widely accepted that you do not play around with bullet weights in these rifles otherwise port pressure goes out the window as does reliability of the op rod and bolt system.

Do not shoot factory 180 grain cartridges in these systems they will eventually become overstressed and something will fail.

Oh yes -- they will shoot 180 gr pills for some time. But the day will come when that rifle will disapoint you and fail.

Regards
Terry in Victoria
 
lots of speculation here, however , the topic has been discussed at length many times before and if you look hard enough , there's probably a sticky - there's also a thing called m14 match loads on the net where they discuss recommended loads- the only reason that the "old masters" like hungry , mystic et al haven't chimed in is that they've been down this road so many times they're not gonna bother- basically 150 is your low end, and 175 grain is your high, ( you can look up or work up your respective powder charges) with 165 being your high end hunting and 168 being your high end target
 
Based on Specifications, there IS a difference between 7.62NATO and 308Win.

The former is tightly speced around a 147gr bullet at a nominal 2700fps. To function in all manner of NATO bang sticks. SAAMI puts the 308W at 2850fps so pressures are significantly higher. It is common for target shooters to run velocites even higher.

Powders have changed over the years but in all instances I am aware of, lean towards the 'fast' end of the burn range.

That is really important because managing port pressure is key to longevity and also accuracy.

The M305 gas/recoil system is a balancing act and is really finicky. Yes, you can fire 308W in the rifle with no obvious ill effect mechanically but I bet accuracy stinks with enormous vertical stringing.

When the load is balanced for the gas system AND barrel, you can get these rifles to shoot superbly. If your brass is ejecting more then a few feet from the rifle, you are running it too hard for best performance. If you see dings and dents on the case body, same thing.

Going to a heavier bullet WILL tax the op rod and other parts. Will it fail in a box or two, of course not. This is still a mondo built steel action. However, ongoing use will show up in increased wear and tear.

As for headspace, that can vary ALOT from rifle to rifle/lot to lot. I have yet to see or hear about a NORC going too far OVER NATO spec which would lead to head separation on the first firing. The chambers are generous for sure but that is a good thing in a battle rifle.

Shooting factory or surplus ammo shouldn't pose any issues if within NATO specs. bolt action factory 308W ammo may split if the chamber is too big.

If you reload, you just have to work around this. mysticplayer.netfirms.com has my thoughts and info on reloading for these rifles. Follow the instructions carefully and to the letter and you will no issues with your M305.

Enjoy the rifle within its design specs and it will reward you with superb accuracy, dead reliability and very long life.

Jerry
 
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