A) you’re gonna seat with what? Why not just go 6.5-06AI and use a real seater and die set?
B) you’re locked into .280AI brass, or having to build a special gauge to help you place the neck/shoulder junction at the correct location because necking an AI up or down places the neck shoulder junction in a different location than necking a standard cartridge up or down and then making it an AI. If you try to neck it with a bushing die other than a Forster, you won’t be able to get all the to the shoulder. You could probably use 30-06 brass if you sized it in a Forster bushing die. I haven’t used a Forster bushing die.
C) although the difference is minute, the 6.5-06AI is larger than a 6.5-280AI.
D) you’d have to pay for a custom reamer print.
^^^ Seems like a lot of hassle to avoid fire forming. If you don’t want to fireform, there are options that will yield practically identical performance and don’t require fireforming.
There’s not really any velocity to be gained by going from 6.5-06 to 6.5-06AI. You mostly just get better brass life and POSSIBLY a LITTLE less throat erosion. I have a 6.5-257Rob AI, with 130’s and 140’s I’ve chrono’d it running faster than most people ever get out of their 6.5-284’s, and that at 10% less powder capacity. Velocity from the 156gr EOL was unimpressive, but a powder change will likely fix that. I probably just got lucky with a fast barrel, but any 6.5-257Rob AI should match a 6.5-284, 6.5-06, 6.5-06AI of equal barrel length. You pretty much reach the maximum performance of a 6.5mm bore, with a case capacity of 60-65gr H2O. You can usually wring a little more pressure out of magnum cases, and of course, although there isn’t MUCH to be gained, doubling case capacity(think 26Nosler) does yield a LITTLE.
From my gun
130’s 3400fps
140’s 3300fps
156’s 2975fps
If I did it again, I’d lean heavily toward 6.5x55AI, 6.5x57(different from a 6.5x257Rob), 6.5-284, 6.5-06 or 6.5-06AI. All would be easier, yield almost the same velocity, and have minimal disadvantage.
