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Recently I was informed that while 7.62x51 mm NATO and 308 Winchester cartridges look, to the eye, to be the same, they are not. Also, their chamber specifications I was informed are different. Are these statements accurate?

If they are accurate, does one of the two cartridges become marginally safe when fired in the other's chamber? If this is true, which is which? Were I barrelling a rifle and wanted to assure that whichever cartridge was fired in the rifle was absolutely safe, which [cartridge] chamber would I choose?
 

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I have shot both in my DPMS308 308/762 barrel, and my Savage, no problem.....

I have had a semi auto 308 since 1963 and never had a problem with either one
 

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I have heard the same thing regarding the 5.56 and the .223. I had a Ruger model 77 .308 years ago and had fired a very small amount of 7.62 through it with no problem. I then reloaded some of that 7.62 brass and refired it again with no problem, but had more than enough R/P brass so that is what I used
 

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Recently I was informed that while 7.62x51 mm NATO and 308 Winchester cartridges look, to the eye, to be the same, they are not. Also, their chamber specifications I was informed are different. Are these statements accurate?
YES.

Number of 7.62 chambers from those used on LMGs (MG60s are horrible), to different drawings of the barrels which means minor differences in the chamber depending. not an easy topic to define. For the NM M14s, there are 4 different drawings. When I load ammo for a friend with 7.62 military Garands, I always make sure to double check the drawing number. Since I load a lot of .308 for rifles which include several M1As, a TRW M21 and several Garands (both 308 and 7.62 chambers), I can cite the load they like with 4064, LC brass and the 175 SMK. there is a difference in the loads for those rifles.


If they are accurate, does one of the two cartridges become marginally safe when fired in the other's chamber? If this is true, which is which? Were I barrelling a rifle and wanted to assure that whichever cartridge was fired in the rifle was absolutely safe, which [cartridge] chamber would I choose?
As documented by the classic old American Rifleman technical team, shooting 7.62 ammo in a 308 chamber can raise PSI by up to 5.500 PSI, shooting 308 in a 7.62 chamber can result in a drop of up to 5,500 PSI.

Is it safe? Yes... I do it, and a lot of people do it all the time. I do get flattened and crattered primers shooting 7.62 in 308 chambers.
 
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