For those complaining about trimming brass, you should try trimming brass every firing with a trimmer that indexes off the shoulder like a Giraud or Frankford. I got a very nice drop in ES/SD and noticed erratic velocities drop out. I trim every firing now regardless so this is a complete non issue for me personally.
I've run 243 for years and it's a great round. No issues with piercing primers and barrel life can be very good especially if you run a longer barrel and H1000. I'm currently running a barrel with a steady diet of H4350 for my first time just because I'm curious and H1000 didn't give the velocity in this barrel like it has all my others. So far I'm at 1200 rounds on it and the velocity is still the same as it was once it sped up after about 200 rounds. No drop in velocity or loss of accuracy. I'm going to run in until velocity starts to drop. If it goes 1800 rounds (which I think it will) then I'll be calling BS on it being a barrel burner even with H4350 as that's right in line with the other 6mm's that shooters run.
I'm not switching from 243 for my 6mm because I'm so invested in brass and dies, and I don't have to worry about the large firing pin in my AXMC piercing rounds. I just don't see anything else doing anything any better. Not saying others choices are wrong either though.
6SLR has always interested me, but forming brass.... meh. If I was going to go to anything else it would be 6 creed or 6x47L, probably 6 creed.
BTW the new Starline 243 brass is excellent and only a little over $400 for 1000 pieces shipped.