Hey Masek,
I'm going to be shooting CBA BR matches this (hopefully) summer with a 7.62x39, and I'll second what others have said about the Lapua and the Winchester brass.
I bought 200 pieces of Lapua brass and sorted it all by weight. 70-80% of it was within a plus/minus 0.3gr range. The high was 126.4gr with a low of 125.1gr and the mean around 125.7gr. The mouths were all factory annealled, as I suspect that most folks just buy this stuff and reform it into a PPC. These have the large primer.
The Winchester brass has been relegated to backup or offhand brass. I began to weigh and found the inconsistency to be disturbing. In addition to this, the primer pockets gave a very inconsistent feel when seating a primer. Some almost fall in, while others scrape hard as they're being rammed in. These also have the large primer.
My rifle has a .308" bbl and shoots well with .310" and .311" GC (sized) bullets. I"ll further second that you need to check your bore to determine what diameter works the best. I'll go on to say that when you buy your reloading dies, make sure that they have the correct components for the bullet diameter that you've selected, as some don't.
I'm searching for some small primer Remington to experiment with, but the quality of the Lapua brass makes me doubt that the large vs small primer comparison is going to offer much in the way of enlightenment.