Re: .280 ackley build
I am building a 280 AI also. Blueprinted 700 action with a Bartlein M24 (.9 muzzle) 26" finish, holland .25 pinned recoil lug, timney trigger, and a manner MCS-T2A, NF scope base, badger rings, and viper vortex pst 4-16, atlas bipod.
I asked the same question the other day about barrel length, and from everything everyone said, and everything I could read, 26" is the most efficient option. I do think a 24" will definitely work, but an '06 needs about a 24-26" since its a longer cartridge and has more powder space than a .308, it takes longer to burn the powder up, since a 280 is a necked down '06, It is logical to assume it could even take more barrel length to burn all the powder efficiently.
Just my 2 cents though.