I've been around a few of these cartridges I built the 6X47 (6-222 RM) first, used a slower twist barrel (1:12) than I should of. However, it hasn't stopped me from killing deer, pronghorn, prairie dogs, and coyotes with it. Loves 70 grain NBT at 3000+ fps and 80 grain Speer SP bullets at 2800+ fps from a 20" barrel. It doesn't do well with bullets over 80 grains is it's only problem.

I shot some prairie dogs and a coyote with my buddies AR in 6X45 and made me want to build one. I built it mainly to get around CO 6mm minimum requirement for big game and brass is easier to find than for my 6X47. I also went bolt action to get a little mor mag length than what my buddy got with his AR. Too bad my suppressors showed up, and I don't want to cut down the barrel to a managable length since it is fluted. My buddy has killed a ton of deer with it and the 85 grain Sierra HPBT.

I've also spent a little time behind an AR in .25-45. Cool little cartridge as well. Dies are probably a little cheaper than the .25-222 to get as well. I will say speeds were not as good as advertised on the web, mid 2700 fps with 87 grain bullets was the best that AR would do.