The 260 Ackley with standard throats and even seated to standard short action lengths will do anything the 6.5-284 will do with less powder. My 260 Ackley is built on a long action with a Mcgowen barrel. I'm running 140 bergers at just off the lands at a c.b.t.o. of 2.217" even though its on a long action it would still fit and feed fine from a short action. I don't feel like I am giving up any performance by having the bullet seated slightly deeper than I would like but its nice to know I have plenty of room to chase the lands as the barrel wares. Using Lapua brass and 42grains of H4350 I am getting 2950fps out of my 26" barrel. For comparison I am running 57 grains of Retumbo in my 6.5-284 with the same 140 berger to get 2960fps. Barrel life, recoil and efficiency is all better with the 260AI.

I also have a 6.5-06 Ackley improved built on a winchester model 70 with 140 Bergers seated to mag length and I am getting incredible performance out of it. Using 59.5gr of H4831 I am getting 3180fps. This is my long range hunting rifle and it does not leave me wanting for more gun at all.