Has anyone ever done a straight neck up of a 6mm Remington case to 6.5mm. I know it's almost the same as a 6.5x57 Mauser, but... the shoulder is different and i will be shooting this in a modern action. The goal is to get 2950fps in a 30" barrel with 142gr. SMK's. Please, no speculation here. only post if you have done this or have been present for the range/chrono testing of this. Thanks in advance for any healpful info.

Take a look at the 260AAR (257AI necked up).

get ackley's handbook. there's several ... is not a matter of actually being there, theres been 10 of them ...6.5x57 ai .. there you go, it'll go as fast as you want ..

of course the 6.5 brenneke is vastly superior 6.5x06 more or less

my 6.5x270ackley started it's 2cd life as a 6.5x57ackley by short chambering a 6.5x.270 ackley reamer. my dies, from redding, are stamped "6.5x257 roberts improved 40 deg" (shoulder). i loved it and foolishly thought i would love more case even more.... had the reamer pushed in to a full length chamber.
2900 with the 129 gr. hornady in the 57mm. case was a piece of cake, should have left it alone! all it does better now is belch fire.

I have a 6.5-257 roberts improved. With a 18" barrel and all the 50 gr H4831 and the best it will do is 2800 fps with 120 gr bullets. The barrel is pretty short (not my choice) so a longer barrel is a good idea. Too much muzzle flash for me.

I shoot a 6.5x284 at long range targets, f-class, etc. Using IMR-4831, Fed.210 primer, lapua brass, Sierra 140 or 142, 26" bbl. Brass life gets very short if I try to exceed 2950 fps. I see quotes of velocities exceeding 3,000 fps. but my rifle won't do it unless I'm willing to discard my brass after 2 or 3 loadings. I also get the best accuracy at 2950 fps. Barrel life with these cartridges is also a consideration as it's pretty short.