Re: How many groove barrel for 7mm wsm
The only real test of groove count is to first determine what the bore and groove diameters will be.
Second, what will be the width and shape of the groove that also forms the lands as well as the cross sectional area. of the hole in the barrel.
Third, agree on the ammo to be used and peak pressure level to be used for testing velocity.
If any comparison's not made to these standards, the velocity numbers will be bogus.
The reason 4 grooves have been the standard for decades in 30 caliber military barrels is their depth, shape and width require minimal engraving of the bullet and weakening of its jacket as well as long barrel life and good accuracy along with easy, efficient manufacturing tooling. Other types start changing things.
When Sierra's 30 caliber 155-gr. Palma bullet was introduced, several folks tried 5- and 6- groove barrels that shot heavier ones very accurate. Neither shot them as accurate as 4-groove barrels.