I would give the thunbs up for a straight up 243 or the improved version. Reasons why? The 6BR looks really nice but is not really big enough to do anything but shoot varmints and this it will do very well. The standard 243 built for Lapua brass would be a sure winner. It will do everything the 6BR can and give you about 200 fps more which should make a better Antelope/Deer rig if you so desire. The improved version will give you even better velocities and less case stretch but you will need to fire form all your brass so right there atleast half of your shooting will be at standard 243 velocities. The 243 will also feed much better through the magazine than an improved version. The AI will feed but expect dented up brass. Remember you can always down load the larger cases which is a much better option than overloading the XC, BR or variant.
I think it depends, to some extent on the length of your action. You mentioned an advantage on trimming necks with the 243AI, but the same is true with the 6/250 and if you have a medium length action, you can really seat long bullets way out there and still fit them in the magazine. The performance level is probably adequate, but you really didn't state your application, targets or live animals?
I once had a 6/250, very sensible choice, if you have any consideration for barrel life, at all. Probably does not require as long of a barrel as the 243AI for optimum performance?
Good hunting. LB
edit: I am a big fan of the standard 6MM Remington, have had three. No flies on that puppy.
The application will primarily be varmints 1100 yd and in. I already have two hot rods in the 270 AM and the 300 RUM. I need something a little more economical to shoot w/less recoil.
I don't care if I can load from the mag. A single shot is ok by me.
BBl life is a major concern. As long as I hit 2800 fps w/the 105 Amax, I'll be smiling. I am just curious if the bbl life of the 6-250 will be that much more than the .243 or .243 AI loaded to sensable pressures? Also curious as to how ofter I'll have to trim the 6-250? It's not like trimming is that difficult, I just hate it!!!
I guess what it boils down to is the fact that the dies I want for the 6-250 are $200!! I guess maybe I should quit being such a lazy, tight wad and just order the dies.
The 6/250 is an Ackley, which means no trimming to length, just like the 243AI. That 40º shoulder reduces forward brass flow to almost nothing.
I'd consider getting Wilson hand dies and buying an arbor press. I don't think that would run $200?
But, barrel life should be noticeably, to significantly better than the 243AI, depending on how hot you load it?
They are both good, but I am sure the 6/250 is more economical and the performance is close enough to a 243W that you wouldn't notice it. (edit: the reason being that you can usually load an Ackley to higher pressures than the 243)