For a SHTF scenario, how many engagements are going to be at 1000 yrds? Unless I shoot out over the ocean here, I don't see the application. I do think for actions within 50 yards, a 12 gauge will be just fine, or an AK or an AR 556. Inside the wire, "say hello to my little friend", no further comment.
I took out a coyote moving at a dead run at 1760 yards off my south deck a few weeks ago with a 6.5 creed. My 308s won’t do that. If four of my buddies didn’t witness it, I don’t think they would of believed me. I get them at 1000 yards plus or minus a bit quite often, but that was the first at that range.
In a semi platform, the difference is large too. 308 will buck fairly well, while 6.5 is a lot less and you watch your rounds going. They hit with about even kinetic energy up to 500 yards, then far exceed 308. Actually even weight bullets, the 308 was hitting at 1000 ft lbs at 500, the 6.5 was at 1350.
I’m a subject matter expert. I usually shoot a hundred or more rounds a week if I’m taking it easy, and have been using 6.5 since 2008. I recognized early on the superiority of the round, and so did the US Army.