Thread: 6.5 what

I shoot a 260 in M7, yes you are right they do have a thin barrel, and are a bit limited for mag length, but there in lies the rub, its a light rifle.
You want a light bush style rifle that will on occassion shoot to 500. Maybe two projectile styles would suit.
I shoot 120 Amaxes, they travel fast and do good on lighter animals ( I wouldnt use them on a Red stag.... but I dont trophy hunt ) For more wind bucking the 140 Amax/ ELDM is good out to 600 yds.
With a bit of experimentation on where your different bullets throw you could dial / hold for the two different weights.

The 120 Grain bullet will seat out pretty far and the 140's I hand feed and are seated long. I dont really shoot animals at distance though only paper.
All you want from a thin barrel is first shot dependabilty and maybe 1 follow up.

If you go the M7 route try the rifle for accuracy first. Mine isnt much chop for 5 shot groups but will happily pull small 3 shot groups.