Hey Jim,
My father recently gave me a Winchester Model 88 [civilian lever action sporting rifle] chambered in .308 [Winchester]. I’ve acquired a few rounds of 7.62×51 ball from a separate source. Can I use that ammo in the rifle? I’ve Googled to no avail. Can you help? Thanks, – d’Heat
JWR Replies: The short answer to your question is: Yes. From a precise technical standpoint, they are not identical cartridges. Military 7.62mm NATO [1] is almost dimensionally identical, but actually a hair longer than the SAAMI dimensional specs for .308 Winchester. Military 150 grain full metal jacket (“ball”) loads have lower chamber pressure than commercial 150 grain .308 Winchester hunting loads, and military brass is thicker than civilian brass. So what you mentioned doing is certainly safe.
All US military ball and nearly all of the European 7.62 NATO is non-corrosively primed, but keep in mind that tracer and incendiary loads leave a corrosive residue. (Clean your bore, chamber and bolt face three days in a row after firing anything suspected of being corrosive.)
You may be wondering: “What about the other way around”? I generally do not recommend shooting .308 Winchester commercial hunting loads through a military 7.62mm NATO rifle–especially a semi-auto. The specification for military rifle chamber length is 1.645 inches, versus 1.632 inches for civilian .308 Winchester chambers. The 0.013 inch difference may not sound like much, but the stress on commercial brass–which again is thinner than military brass–could conceivably cause head separations if fired in a military or paramilitary rifle such as an M1A, FAL, L1A1, or AR-10. This is especially true for handloaders that use brass over and over. For this reason, I exclusively use once-fired U.S. military match grade brass for all of my .308 handloads. That way we can use the same ammo in any of our L1A1s, in the Memsahib’s .308 Valmet, and in our various .308 bolt action rifles.