My thought is to stay with the 6.5 bullet to keep the B.C. up at 140gr.
But I couldn't see using the .284 case or the 06 case due to the short barrel life.
My solution to this was the .260AAR AKA the 6.5x257 Roberts Ackley Improved.
Close on the heels speed wise to the 6.5-06 or 6.5X.284 and way more barrel life.
I knew building a light recoiling long range gun was going to result in lotsa range time, just because it's so much fun. I didn't want to worry about using up a barrel prematurely.
My next project will be the .280AI though. I don't see how a person can do wrong with any of these cartridges, given their budget for barrels and 'smith expenditures.
I have hunted with a 6.5-06 A.I. for 25 years and now shoot a 6.5 Sherman which has 100'/second more velocity. They are a great rifle! I have killed approx. 25 bull elk, numerous deer, black bear and one moose. Since the B.C. of a 140 6.5 bullet and a 160 .284 bullet are very close and the velocities are similar, the difference between the two is foot pounds pure and simple. Both are capable of killing anything on the North American continent that sleeps but the .280 will do it a little further.......Rich
I had Kirby Allen build me a 6.5-06 AI on a Lawton action about two years ago. Although the barrel had a 1:8 twist for the 140 gr. bullets, the barrel ended up liking the 130 gr. Accubonds better. Not quite the BC of the 140's, but better transfer of energy on the other end (IMHO). Very accurate and seems to knock the stuffing out of whatever it hits. The 130's leave the barrel at 3,115 fps. Just completed a black bear hunt. Hit him at 250 yds. across a steep canyon and it rolled him. Never took another step - lights out. Weighed in just a tad over 300 lbs. Same result for two deer and numerous coyotes.
Either caliber will get the job done. Yes the 280 AI can be loaded up above the 140 grainers; but likewise, the 6.5-06 AI can be loaded down to 100 grain (Nosler ballistic tips). And believe me - that bullet is light recoiling and really hums.
About four years ago I built a 6.5-06, I use 140gr. Hornady Interlocks, which it likes very well. Last year I built a .280AI and have used 140 grain Noslers for load workup. Have not had a chance to take any game with the .280, however, had great success with the 6.5. It simply works.
I am shooting a new 6.5-284 this fall with 140 gr Accubonds. I can't tell you how it preforms on game...yet. Hopefully I'll be able to fill you in after my MT elk hunt next week.
In terms of .280AI vs. 6.5-06, my gunsmith friend shot a .280AI for several years and loves the rifle. He is now shooting a 6.5x47 Lapua. No , it is not the 6.5-06; however, with a max load of RE 17, he is not far from 6.5-06 velocity (~75 fps) shooting 140 gr bullets. He does like that the heavier .280 bullets will buck the wind a bit better, nonetheless, the .280 is sitting in the safe while the 6.5x47 is in the field this fall. His 6.5 is a lighter rifle with less recoil and plenty of "oomph" to take all the critters he hunts in MT...including elk.
I vote for the 6.5. I am not convinced that the AI in this particular cartridge is worth the effort. I am not against fire forming, I do it now. Just not sure if the gain in the 6.5-06 is worth the time and money to get there.