ORIGINAL: Roskoe
I have, in the past, owned both the 6MM Rem AI and the .243 AI. Both are real nice calibers, and produce around 175 fps more velocity than the parent case. Brass life can be very good as well, with no need to ever trim cases.
But if you are looking for a high performance 6MM, the best of the lot is the 6MM-284 - in my opinion.It is a little better caliber than the .240 Weatherby; and now that Norma and Hornady make brass for 6.5-284, there is a readily available supply of high quality cases that require minimal work to neck down. The old .284 Winchester cases worked fine, but they needed to be necked in at least two steps and are not as consistent as the Norma cases.
That's what I thought too, however, I'm having all kinds of problems with my 6-284. So far things have not gone well. It's back at Competitive Edge now having the bedding checked and safety/trigger worked on. I've never had so many problems with a Mauser action and Sako barrel the thing should be a dream......right now, it's a nightmare! One thing for sure the go nogo gagues say good to go.....the rifle is just a basket case......more to come and hopefully, better news. OBTW, I don't see why a Ackley shoulder would reduce pressures....When you get the extra speed there must be a higher resultant in pressure. I love the Ackley shoulder but you just can't load one up and not expect higher chamber pressures. From what I've read and experienced with a 6.5-06Ackley, 257 Ackley and '06Ackley you get about 100-150'/sec without pressure problems. Really not bad enhancement for all the other benefits already mentioned. Regards, Rick.