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Here we go again, maybe?...

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Goosic View Drop Down
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    Posted: November 23 2022 at 5:21am
Preface: It is to be assumed that the 7.62mm chambered rifle a user owns is in safe operating condition. 

Originally posted by The Armourer The Armourer wrote:


Had you considered that commercial 308 cases are very different specification to 7,62 NATO spec cases ?

Case wall thickness is much thicker on the 7.62 compared to 308
7.62 chambers are 13 thou (0.013") longer than 308 meaning that these thin-walled 308 cases stretch and can split.
The case volume on a 308 is greater than a 7,62 leading to different powder burning characteristics

(*Throw in a 'bit of extra powder' and you have an accident waiting to happen.*)

Let us address that last comment made by The Armourer first and foremost shall we.

For those Brand New to and starting out in the reloading world. NEVER under ANY circumstances just "Throw in a bit of extra powder."

The Armourer. Yes, the .308W is not entirely identical to the 7.62x51mm NATO, owing to differences in tolerances; (Mainly meaning that the differences are in the actual .308W & 7.62 rifles chambers respectively) and therfore, some commercial rifles will not handle military ammunition.
However and be that as it may. Even with the differences in case wall thickness/case volume between commercial and military brass respectively, as long as the reloader stays well within the published guidelines of his or hers chosen reloading data and NEVER exceeding the max charge weights, reloading for the 7.62x51mm NATO chambered rifle using .308W commercial brass and using projectiles of 175grn's or less, (cartridge capacity and overall cartridge case length are not well suited using projectiles exceeding 180grn's) should be of absolutely no issue or consequence to the rifle or its user. It is ONLY when a reloader goes against what is recommended that an issue will undoubtedly arise. 
Food for thought Alan: Once a commercial .308W cartridge case has been fired in a 7.62x51mm NATO chambered rifle, that particular cartridge case is no longer to the .308W commercial rifles chambers specifications is it not and no longer having the potential issues of stretching or splitting?...
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britrifles View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: November 23 2022 at 7:27am
We have hashed this one out several times.  But, here's my view, FWIW.

It would be unlikely you will get into trouble using .308 Win load tables from reliable published sources (like powder and bullet manufactures) using .308 Win commercial cases if you stick to the minimum powder charges for your 7.62 chambered Lee Enfield.  I think this is particularly true of the No. 4 7.62 conversions; maybe not always the case for the Ishapore 2A/2A1.  If the load tables give pressure data, pay attention to it. 

You may well get into trouble if you load your LE 7.62 with max .308 Win published powder charges using 7.62 military brass. I certainly wouldn't do it, that goes against reloading manuals that recommend reducing the charge when using military 7.62 brass.  Remember, the No. 4 action was designed for the .303 British cartridge, not the .308/7.62.  It turned out that it had sufficient strength margin to handle the higher pressure 7.62 NATO round.  

My last thought is about the long term wear/tear on the action and barrel.  You will be better off loading the LE 7.62 to .303 British pressures.  

  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: November 23 2022 at 9:45am
britrifles. Your very last sentence/comment, "You will be better off loading the LE 7.62 to 303 British pressures." is exactly why I ALWAYS load my 7.62mm/.308W ammunition with the Hodgdon Reloading Data's recommended starting charge weights for the ".308 Winchester Service Rifle" while utilizing ONLY the 168grn Sierra HPBT projectiles. Keeps the Long Term Wear and Tear to an exacting minimum and I am never exceeding that Golden Number of 45,000 CUP...
Sidenote: The published data that can be found throughout the internet legally and through Public Domain lists The United States Military's M852 Match Cartridge of having a chamber pressure of 50,000 PSI using their testing process and a pressure of 44,683 using the Copper Units of Pressure tests. Again. All well below that 45,000 CUP number...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: November 23 2022 at 10:40am
Somewhere I've seen test data for .303 Mk VII Service cartridges using the US radial copper crusher method.  The particular ammo tested was Canadian Dominion Arsenal, I think 1952, and it was around 42,000 CUP.  I'll try to find it.  I wish we had more test data on the Mk VII service cartridge. 

The 7.62 case base diameter is slightly larger than the .303, which gives slightly higher bolts loads at the same chamber pressure; but not enough to worry about unless your near the maximum. 

Not sure I would call 44,683 CUP "well below" 45,000 CUP, but no risk there.  

Interpolating Hodgdon Reloading Data, my VARGET Match Loads (rounded to the nearest 100 CUP):

   .303 - 40 gr, 174 SMK, 41,000 CUP   

   7.62 - 40 gr, 168 SMK, 37,000 CUP (estimate 3,000 CUP higher with 7.62 brass) 

   7.62 - 43 gr, 175 SMK, 44,600 CUP (for 800 to 1000 yard line limited use, commercial .308 brass)

The two 7.62/.308 40 grain Varget load is actually a bit under the .308 minimum charge, but this still gives fairly good load density in .308 cases, so I'm not concerned. 

I would consider the 40 grain Varget loads as "maximum" for high volume use in the No. 4 rifles.  For the .303, I've probably shot in excess of 8,000 rounds of this load in my No. 4 I use for shooting CMP matches, and another few thousand in the other No. 4 rifles I have.  No issues at all, no measurable change in headspace, very good accuracy.  



  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Honkytonk Quote  Post ReplyReply Direct Link To This Post Posted: November 23 2022 at 11:01am
Question regarding "parent" cases. Didn't the 7.62x51 originally use the .300 Savage case? My buddy has a Model 99 in that calibre as it was his Dads. Apparently in the day it was the big boy on the block as most of the local farmers had lever 30/30's! They would borrow it when going for moose, Elk or bear.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: November 23 2022 at 11:22am
Experimental tests were done using the .300 Savage case leading to the T65 Series of cartridges, which became the .308W two years prior to the adoption of the T65E5 experimental cartridge that became the 7.62x51mm NATO...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: November 23 2022 at 12:11pm
I think that was very early in the initial development of the 7.62.  The .300 Savage is a shorter case than the 7.62.  My understanding is that the 7.62 was a development from the .30-06, essentially shortening the case taking advantage of the more modern powders that had reduced volume for the same energy.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: November 23 2022 at 12:19pm
Originally posted by britrifles britrifles wrote:

I think that was very early in the initial development of the 7.62.  The .300 Savage is a shorter case than the 7.62.  My understanding is that the 7.62 was a development from the .30-06, essentially shortening the case taking advantage of the more modern powders that had reduced volume for the same energy.  
Taken from a dedicated On-line source:
During the 1940s, the .300 Savage became the basis for experiments on behalf of the U.S. military that resulted in the development of the T65 series of experimental cartridges. The original experimental case design by the Frankford Arsenal was designated the T65 and was similar to the .300 Savage case, but with less taper. The experimental cases were made from standard .30-06 Springfield cases which gave a little less capacity than standard .300 Savage cases because the Frankford Arsenal cases had slightly thicker case walls. The later T65 iterations were lengthened compared to the original T65 case and provided a ballistic performance roughly equal to the U.S. military .30-06 Springfield service cartridge. Over forty years of technical progress in the field of propellants allowed for similar service cartridge performance from a significantly shorter, smaller case with less case capacity.[2][3]

Winchester saw a market for a civilian model of the late T65 series designs and introduced it in 1952, two years prior to the NATO adoption of the T65E5 experimental cartridge iteration under the 7.62×51mm NATO designation in 1954. Winchester branded the cartridge and introduced it to the commercial hunting market as the .308 Winchester.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Honkytonk Quote  Post ReplyReply Direct Link To This Post Posted: November 23 2022 at 12:49pm
Thanks for the clarification!
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