Re: 6mm 115gr berger in .243win
Hi if your barrel is a true 8 twist you will have no problems some barrel manufacturers state the button twist rate that they ust not the finished twist rate. with cut rifles barrels the rate is almpst exact but with button rifling their is allways some button slippage this can be from 14-1" diference in button rate to finished barrel depending on the procedure and twist being made.
Ask your barrel manufacturer what the Finished twist will be.
I have just finished testing a 6X47 Lapua in an 8 twist barrel with 115gr Bergers and 107gr Sierras and both performed very well. the 107's are around 3100fps and the 115gr Bergers are at about 2950fps. Do not push the 115gr Bergers much past 3000fps as you will end up blowing them up they work very well at 300fps or below.
If you dont have the barrel chambered yet take a good look at the 6.5X47 Lapua necked to 6mm it si an awsome case and will do what you are after with the ability of feeding the heavy VLD projectiles seated out through a standard mag and it has a 30 degree shoulder instead of the 20 degree shoulder on the 243.