I have the Lyman Pistol & Revolver Manual. In 308 Win with 15" Barrel it shows a Maximum velocity of 2618 with a 150 grain bullet using AA-2230. It also has 43.5 grains of IMR 3031 maxing out at 2596 fps.
Lyman lists 47.0 grains of Varget only making 2505 fps.

My Sierra Handgun Manual shows only one load using 49.0 grains of WW748 getting to 2600 Fps. Sierra was using a 14-1/8" Pachmayr Dominator to work up their loads.

The Hodgdon Loading web site has much higher numbers listed with a 15" Barrel.
IMR4064 has the top velocity with 47.7 listed at 2681 fps. Varget is listed at 47.0 grains making 2675 fps, and 43.5 grains of IMR 3031 maxing out at 2659 fps.

DATA DISCREPANCT:
We have Lyman's 43.5 grains of IMR 3031 only doing 2596 fps, while Hodgdon's 43.5 grains of IMR3031 is maxing out at 2659 fps.
Lyman's 47.0 grains of Varget is maxing out at 2505 fps, while Hodgdon's same 47.0 grains of Varget is maxing out at 2675 fps. Hodgdon must be doing something a lot different in their testing methods. I believe Lyman was using a 15" Encore to work up their loads. Hodgdon's web site just says 15" Barrel.

I did a lot of searching on line to try and determine what velocity folks were getting out of a 150 grain 308 reloading. I did not come up with a lot of numbers, but what I found were lower than expected.

WHAT I AM WORKING WITH
I am working with my 15.875" Stainless Steel MGM Encore barrel in 7.62x54R with .308 Bore, and a Four Gill Muzzle Brake. I would think that the 7.62x54R should produce velocities equal to the 308 Winchester, if not a hair higher considering case capacity is pretty close to the 30-06 Springfield.
I have only worked with IMR 4895 so far this round with 150 grain Speer #2023 Flat Base, Hot Core Bullets. My highest velocity load 49.5 grains of IMR 4895 is producing 2583 fps with an SD of 31 fps. Comparing my velocity numbers with the 308 Winchester in my Lyman and Sierra Handgun Manuals my load is not doing bad at all compared to the 308 Winchester.

Compared with Hodgdon's On Line 308 Winchester Handgun Load Data, and Sawfish's numbers I should be able to get higher velocity with a different powder. What powder to work with next? I have AA2015, TAC, WW748, IMR 8208, IMR4064, RL15, RL17 and a few others that should work reasonably well in the 7.62x54R.

Looking at NEW Rifle Date (Speer Manual #15) for the 308 Winchester it looks like Alliant Power Pro 2000-MR would be worth working with, if any could be located to try out. It is doing nice things in 308 Winchester as well as 30-06 Springfield Rifle Loads. If the highest velocity rifle loads are also the highest velocity handgun loads, this powder should bring the 7.62x54R speed up a little more than I am getting with IMR4895. Possibly quite a bit more.

Bob R