Re: f-class build that caliber would u go with?
The .260 Rem is a really popular chambering, but I tend to agree with some that it (and the 6.5CM) may be borderline inadequate compared to the 6.5-284 and such.
While the US Team may be moving to 7mm magnums, that won't help you with your .308 (.473" Diameter) bolt face. I do applaud the move to 7mm, but for that bolt face, the .284 Win and .280 Rem are more suited.
Yes, there's no denying the .280 is a long action cartridge. But for a long range comp rifle, magazine feeding is neither mandatory nor especially desirable.
A .30-'06 length cartridge, like the .280, can be successfully hand fed and chambered from a short action.
The fired case can be extracted and ejected, but an unfired one needs the bolt stop to be released so the longer cartridge can make it out completely.
Unless you're doing this a lot of the time, it's really not that hard to accommodate. This allows a LA cartridge to be used as a reasonable chambering option with a switch barrel SA rifle.
The .280 can work, and it matches your boltface diameter. It's not a wildcat, has reasonable bore life, and commercial hunting ammo is relatively available. A 1:9" twist will handle up to 175gr bullets, and the case will drive them and lighter bullets at very respectable speeds. For F Class it is already beginning to be seen; and from what little I've been able to read about it, the chambering is quite competitive. You can conservatively expect BC's of well over .5 and velocities well above 2850fps.
Greg