I'm going to replace the 24" Shilen (Sporter Magnum contour) with a Krieger Palma contour cut to 26" in a 1:8 twist to handle the 140 gr bullets. I use the rifle for competitive Tactical shooting out to 1000 yd. I've been loading the Lapua brass with H4350 (46.5 gr) and am getting just under 2900 fps. Anybody have an idea about what the increase in velocity might be and if I should change to a faster or slower burning powder? Also, I've been using Berger bullets exclusively but have had stability problems in the past and was wondering if there was a more compatible bullet out there for long range use?

Thanks,
Bill

IMO you're using the right powder. Faster or slower will likely be less velocity....how much?....anyones guess.
I also doubt that you'll see any difference in velocity because of barrel length difference of 2"

You might want to try Sierra 142MK's in that caliber for it is quite common for long range use. Lots of folks use Bergers and sure they are a good bullet, but whatever bullet you use will need to keep the terminal velocity super sonic or you will have "wobblers." If you can maintain velocity of 2900fps plus you can check a ballistics program to get an idea as to velocity at the 1 K mark. Believe it will be somewhat more than 1250fps which is workable or stable if you will. Are your Berger's VLD's??

You can expect about 30 fps increase in velocity.

Since this is a norwegian/swedish cartrigde we use it a lot up here in Scandinavia. The long range shooters in Norway use the 6,5x55 out to 1300 yards.

The stability issue you mentioned might very well disappear with the switch in barrels. And I agree that 4350 is about the perfect burning rate to use with 140's in the 6.5X55, but believe you might be better served with V-V's high energy series of powders. N550 and N560 almost exactly split the difference leaving H4350 in the middle, and would make for a grand experiment with your new barrel. I wouldn't switch away from Berger bullets, not unless your stability issue reappears.

N5 series powders are very harsh on barrels. I have heard this both from match rifle shooters, smiths and seen it in my own sporting rifle which has a very warn throat from approx 1.5kg of N550 down it.

IMHO the velocity isn't worth the wear in a custom barrel.

Thanks for the input, fellas.