I shoot an improved 6/250. Similar but improved . It'll push a 105 grain Amax at 3000 fps without going into over pressure, but would still consider it to be about as close to max as I wanta be. The 6XC is really nothing but a necked up 22-250, or a necked down .250 Savage case. the 6XC and the .243 both have similar issues, and the improved versions only marginally help fix the issues. They both show a neck length that's very close to .250", but you will find that it often comes out a little shorter than that. If you do the improved case, expect a neck length to finish out at about .230". The 6XC will be better in the case shrinkage department, as there should be very little. The shoulder angle is not so hot on either round. I planning on a 1200 round throat life in my barrel; which is far greater than a .243. But sorta lackluster compaired to a 6BR that will easilly go 2500 rounds.
I know two or three guys that have been shooting the 6XC (or it's clones) over the last fifteen years or so. Most are shooting bullets in the 75 to 85 grain range. I think they are getting around 3250 fps with 80 grain bullets. That's pretty close to a .243. But a 6BR will also push an 80 grain bullet to about 3100 fps! With a lot less powder. I use .243 cases to form the 6/250AI, and I do this to get better cases with less case shrinkage ( you won't worry too much about that). But when this barrel finally goes south I'll rechamber it in 6BG. Very similar to the 6/250AI, but with a longer neck and a 30 dregree shoulder. The shoulder comes in at 1.552" verses the 1.514 of the 250 case.. I think I do all this with about a 1/8" set back and still clean up the throat damage (if not I'll go .25") The over all length will finish out right at what the standard .243 case length is, but with a .35" neck. But I'm tempted to ream the head space a little short to come in with a 1.48" shoulder length instead of 1.552". In otherwords a 6mm Int. on steriods with a 2000 round barrel life.
I'd be skeptical about the claim of more accurate than the 6 BR. If you go to 600 yd match reports you will see 6BR or it's variation 6 Dasher etc. winning far more than anything else.
I'll agree with you! I can't see it being more accurate, but with one exception. That would be out past 500 yards. Pindell once said that past 300 yards the 6BR was a better round than the 6PPC, but the 6XC has a about 5 to 6 grains more capacity so that has to help a little bit. But that changes with the 6BRX, or the Dasher. The Dasher is a pretty good round, but there were a few complaints a couple years back on B.C. over barrel life and split case necks. Never been around one, so I don't know if that's crap or not.
You can get the 6XC brass in Norma which is very good. You won't have to fiddle with necking/reforming in 6XC.
It is larger than the 6x47L and matching the 6-Creedmore capacity. Slightly bigger still is the 6CM, which invokes much cooler H1000 powder(to best all these in barrel life).
There is the difference in primer size, which comes into play for competition loads with a 6x47L(very hot) -vs- milder loads with heaviest of bullets using a 6XC.
I believe this results in better accuracy from a 6x47L(matching 6Dasher capacity & accuracy) through mid ranges, but leaving an edge to higher BC 115gr bullets at 1kyd from a 6XC (only in the wind).
I shot a 6XC for maybe 10yrs, and still shoot 6BR.
Beyond terminal ballistics, while not minding necking/reforming, I'd go 6Dasher or 6x47L. Both Lapua brass, and small primer pockets.
Not that there is anything wrong with the 6XC. It really is a good & easy cartridge.
It's just that you can't push very hot loads with it for long, and there are accuracy benefits to hot loads -with the right brass & cartridge design.
With Norma brass, 6XC capacity, and large primers, you can't run hot loads without chasing your tail. I don't know anything about Creedmore's brass.