So here's the rest of the story. The rifle is an Argentine Mauser bolt action 30-06 my grandfather built with a 28" barrel. I have no idea when it was built, but my guess is before I was born in the mid-70s. It seems the theory behind the build is to maximize powder burn and velocity for the 30-06, but it's not a heavy barrel profile for prone only shooting. It can actually be shot offhand, although it is heavy and unwieldy due to the length. I don't handload for 30-06 (yet), but I have been disappointed with factory ammo accuracy as well as the left over handloads my Grandfather gave to me. They're adequate for hunting, but nothing spectacular like cloverleafs which I would expect from such a long barrel. The muzzle is .645", so I'm guessing there might be a lot of muzzle whip. I'm trying to figure out what weight bullet would be best through a long barrel like this with a 1:10.5" twist rate. I'm guessing something like the 175 SMK or 178 SST from Hornady. What do you think?