[Unclenick]

To address your inquiry, go to Hodgdon's web site. They now distribute IMR, too. Go through the steps to get .308 load listings up. Then, in the upper right there is an option to print the results. When you print them the case and primer and case trim information are included.

Lapua cases weight about 172 grains. Winchester weighs about 156 grains. That is a difference of 16 grains. Divide that by the density of 70:30 cartridge brass, which is 8.53, and you find you have not quit 1.9 grains difference in water capacity. IMR4064 has a bulk density of about 0.87, so this is just over 1.6 grains difference in powder capacity. It is enough extra volume that you can add around one extra grain of IMR4064 powder to the Winchester case so it will reach the same peak pressure as a load developed in the Lapua or Federal case will.

The length of the barrel affects velocity, but peak pressure occurs after the bullet has only moved maybe two inches, so as long as your barrel is longer than that, you won't have an issue with affecting pressure. The extra length will let the lower pressure present near the muzzle accelerate the bullet a little more. You might gain an extra forty fps from the extra two inches of barrel.