Re: What benifit does a tight bore barrel have
All depends on what ya'll mean by 'tight bore'...RJB is correct, palma barrel groove diameters were changed to .3065-.307" due to the RG 155's .307" OD...They dropped the bore size(land diameter) to .298 to give longer barrel life over standard .300(deeper lands to wear thru, as a barrel shoots out from chamber to muzzle generally)..When Sierra picked up the Palma, the bullets were and are running at .308", so groove diameters have followed suit in .3075-.308, but many are staying with the .298" bore diameter, to once again give better barrel life..Some are still shooting the .308 bullets in the .3065" barrels, but I wouldn't recommend this, as your bolt might get a bit sticky, ha..
Sometimes people use tighter groove diameters because they are using shallow throats, and don't want the grooves to shadow into the throat..
You don't necessarily get a tighter seal with a tighter bore, higher pressures maybe, because gas is going to escape around the corners of the land/groove intersection in conventionally rifled barrels..A tighter bore by itself in conventional rifling can lead to bullet upset as metal is not compressible, flows in length, so your bullet will get longer as mushes it's way thru the tight bore, and you will still get leakage round the corners..If you cant the lands a bit, or radius the intersection, or polygo-fy that gives you a better seal between bullet and bore..
That's my story and I'm stickin to it..ha..