So I did a little experiment today that I have never tried before. The twist rate on a rifle I own was unknown, so I coated about 14" of a cleaning rod with masking tape, attached a cleaning patch to the end of the jag and marked necessary points on the masking tape. After trying 4 times, I came up with the same answer 3 times...10.5" for 1 full rotation. I believe the time I came up with a different answer I over-rotated. That seems like an odd twist rate. 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?