M14 and M1A Talk M14 and M1A rifles - General Posting

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Old 12-02-2008, 09:15   #1
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7.62x51 vs .308

I am confused on the differences.
7.61x51 has a longer neck. So the part of the brass that actually touched the bullet is longer?
Also the cases are thicker, therefore has less capacity?
My SA M1A is not marked for either caliber. The factory says it has a headspace of 1.6347 or so and it hasnt been fired.

I only ask because ive got 1k of 7.62 LC brass, all 04-05, that are going to be my M1a ammo. Ive been told I need to size using a small base die. I dont have that. Ive got a dillon .308 size/trim die, and its full length as far as I know.
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Old 12-02-2008, 17:18   #2
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If your reloading (and it sounds like you are) the only difference you have to worry about is the case capacity (assume mil brass has a lower capacity, so back off 1-2gr from "comericial" brass data)

Now, the difference in the 2 chambers is that the Mil chambers have a longer throat.

The above statements will get all the "internet experts" all exited, but if they would learn HOW to read a print, they would realize that the 2 cases are externaly identical (the much touted headspace measurment difference NEVER notes that the datum circle is a different diameter). Base to shoulder, base to neck, shoulder angle and shoulder diameter are all the same, comericial gauges measure closer to the shoulder while military gauges measure closer to the neck.

As far as "needing" a small base die, all you can do is size a few and try them in your chamber. If you have to buy a SB die, simply install it where your FL die is now (you use one or the other, not both)
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Old 01-04-2009, 21:56   #3
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Tailgunner,
finally your the only other person so far that knows the rounds are basically identical except for pressure and case capacity due to brass thickness. As to the post you should find out if your rifle chamber is .308 or 7.62x51mm. Rule of thumb is that you can shoot 7.62 milspec out of a .308 bore but not .308 out of the 7.62 milspec chamber. The only reason this is generally followed is that most .308 ammo is loaded to a slightly higher pressure than Nato 7.62. Keep in mind that both rounds are measured slightly different as far as pressure is checked. Tailgunner chime in if you know exaclty but I think Nato is measured in CUP pressure and .308 in PSI or vis versa not positive but the reason you are not supposed to shot the .308 out of a nato bore is because that barrel/bore was not tested to the slightly higher pressure of the commercial .308 bores. I myself have a POLYTECH M14S which has a .308 chamber and I shoot both Nato and commercial as well as my oen handloads with no problems. I also know people who shoot .308 out of Nato chamber rifles. Its up to you but to know the chamber is the first thing I would fins out from the manufacturer if its not labeled on the barrel. Just my knowledge and 2 cents put in but I am fairly sure that my info is accurate. If I am wrong someone please chim in cause you can always learn something new.

Originally Posted by Tailgunner View Post
If your reloading (and it sounds like you are) the only difference you have to worry about is the case capacity (assume mil brass has a lower capacity, so back off 1-2gr from "comericial" brass data)

Now, the difference in the 2 chambers is that the Mil chambers have a longer throat.

The above statements will get all the "internet experts" all exited, but if they would learn HOW to read a print, they would realize that the 2 cases are externaly identical (the much touted headspace measurment difference NEVER notes that the datum circle is a different diameter). Base to shoulder, base to neck, shoulder angle and shoulder diameter are all the same, comericial gauges measure closer to the shoulder while military gauges measure closer to the neck.

As far as "needing" a small base die, all you can do is size a few and try them in your chamber. If you have to buy a SB die, simply install it where your FL die is now (you use one or the other, not both)
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Old 01-05-2009, 04:13   #4
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7.62NATO is loaded to CIP spec, using a Piezzo pressure transducer located in the throat, while 308Win is loaded to SAAMI specs using a Piezzo pressure transducer located aganst the case body. Both are a force/area (p/sq " vs kg/cm) type of reading vs CUP (copper units of pressure) which is a deformation system.
I'm gonna have to rely on my memory of a conversation I had with the creator of "QuickLoad", but IIRC actual pressure testing of both types of ammo using both types of pressure systems shows little or no actual difference in pressure between them.
IOW the much touted "pressure difference" comes mostly from the testing methiod, not the ammo.
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Old 01-05-2009, 16:38   #5
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Originally Posted by rapid223fire View Post
I am confused on the differences.
7.61x51 has a longer neck. So the part of the brass that actually touched the bullet is longer?
Also the cases are thicker, therefore has less capacity?
My SA M1A is not marked for either caliber. The factory says it has a headspace of 1.6347 or so and it hasnt been fired.

I only ask because ive got 1k of 7.62 LC brass, all 04-05, that are going to be my M1a ammo. Ive been told I need to size using a small base die. I dont have that. Ive got a dillon .308 size/trim die, and its full length as far as I know.
Since you say you have a Springfield Armory M1A, let me tell you about my research.

I was a bit concerned once about the .308 win vs 7.62x51, so I called Springfield Armory and asked them if it was ok to fire 308 in my Springfield M1A. Their customer service told me shooting 308 is fine in the M1A. I've called them 2-3 times to make sure I got different people and asked, and all of them told me factory 308 ammo is fine.
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Old 01-05-2009, 17:24   #6
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http://www.surplusrifle.com/shooting...nato/index.asp

http://www.thegunzone.com/30cal.html
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Old 01-06-2009, 17:59   #7
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From Springfield Armory

http://www.springfield-armory.com/as...ory_MA9102.pdf

Note the specs state you can shoot .308 Winchester or 7.62x51 Nato. They state 7.62x51 NATO (.308 Win)
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Old 01-06-2009, 18:47   #8
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Both "articles" are simply reprints of the same eronious information. Neither author ran their own pressure tests in barrels that were test configured to both SAMMI and CIP/NATO specs. Neither one noticed that the location of the transducer is different between the two specs, or what that difference means to the results. Neither one was smart enough to note that the headspace datum circle is a different diemeter, and therefore hits at a different point on the shoulder angle, even though both are actually the same.
The creator of "Quickload did all those things, and found no statisticle difference in the pressures of 7.62 vs 308W ammo in either type of chamber.

IOW, just because a bunch of writers tell you the earth is flat, dosn't make it so.
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Old 01-06-2009, 19:14   #9
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Originally Posted by Tailgunner View Post
CMA
Both "articles" are simply reprints of the same eronious information. Neither author ran their own pressure tests in barrels that were test configured to both SAMMI and CIP/NATO specs. Neither one noticed that the location of the transducer is different between the two specs, or what that difference means to the results. Neither one was smart enough to note that the headspace datum circle is a different diemeter, and therefore hits at a different point on the shoulder angle, even though both are actually the same.
The creator of "Quickload did all those things, and found no statisticle difference in the pressures of 7.62 vs 308W ammo in either type of chamber.

IOW, just because a bunch of writers tell you the earth is flat, dosn't make it so.
I don't think pressure is the real difference, it's chamber dimensions and case thickness/strength.

I have a FR-8 that will close on a .308 field reject gauge (1.638"), but not on a 7.62 NATO field reject gauge (1.6455"). I also have two Enfield 2a's (Ishapores) that will close easily on .308 no go gauges (1.634") and nearly on .308 field reject.

The few times I've tried .308's in these rifles (before I got the gauges) I had sticky extraction. All function fine with 7.62 NATO ammo.

I've never had a problem using 7.62 NATO in a gun chambered for .308. However, besides the sticky extraction in the FR-8 and Ishapores, I had a case separation in a PTR-91 (HK-91 clone).

Again, I don't think this is a pressure issue, but one of a thinner case (.308) in a larger chamber (7.62 NATO).

Likely M1A's are chambered to SAAMI .308 spec so either .308 or 7.62 NATO will work, but this is not true of all rifles.

Last edited by cma g21; 01-06-2009 at 19:16.
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