The Firing Line Forums - View Single Post

Bart B. · October 27, 2012, 07:47 AM

Note that Palma teams around the world chamber their barrels such that the load used in world championships will push Sierra's bullets into the lands a bit. Best accuracy's attained this way according to those who shoot good enough to get on the teams. This is one reason why samples from the ammo lot to be used are sent to them months ahead of time so chamber reamers can be made for that ammo.

Back in 1991 when a few of us worked up loads for Sierra's then new 155-grain Palma bullet, we all seated them about .010" longer than leade contact. The load load selected (45.3 gr. of IMR4895, new Winchester case, Fed. 210M primer) used later that year by several Palma team members from around the world in a big match shot about 1/2 MOA or better at 600 yards in their rifles; note a variety of chamber and bore dimensions were used in those barrels. A picture of a production test group in a fall 1991 issue of Handloader Magazine showed a 20-shot 2.7" group at 600 yards.

A few key elements of the 29 to 31 inch barrels used to shoot them. 1:12 to 1:14 twist barrels shot them the most accurate. 4 groove barrels shoot them better than 6 groove barrels. Groove diameters need to be at least .0005" smaller than the bullet (which was .3084") and some barrels were as tight as .3065" for groove diameters. Bore diameters anywhere from .3000" down to .2980" worked well. The 30" Obermeyer barrel I used to help develop the load and allow me to shoot the high 4-day aggregate score in the match had .3070" groove and .2980" bore with a 1:12.7 inch twist.

October 27, 2012, 07:47 AM	#3
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	Note that Palma teams around the world chamber their barrels such that the load used in world championships will push Sierra's bullets into the lands a bit. Best accuracy's attained this way according to those who shoot good enough to get on the teams. This is one reason why samples from the ammo lot to be used are sent to them months ahead of time so chamber reamers can be made for that ammo. Back in 1991 when a few of us worked up loads for Sierra's then new 155-grain Palma bullet, we all seated them about .010" longer than leade contact. The load load selected (45.3 gr. of IMR4895, new Winchester case, Fed. 210M primer) used later that year by several Palma team members from around the world in a big match shot about 1/2 MOA or better at 600 yards in their rifles; note a variety of chamber and bore dimensions were used in those barrels. A picture of a production test group in a fall 1991 issue of Handloader Magazine showed a 20-shot 2.7" group at 600 yards. A few key elements of the 29 to 31 inch barrels used to shoot them. 1:12 to 1:14 twist barrels shot them the most accurate. 4 groove barrels shoot them better than 6 groove barrels. Groove diameters need to be at least .0005" smaller than the bullet (which was .3084") and some barrels were as tight as .3065" for groove diameters. Bore diameters anywhere from .3000" down to .2980" worked well. The 30" Obermeyer barrel I used to help develop the load and allow me to shoot the high 4-day aggregate score in the match had .3070" groove and .2980" bore with a 1:12.7 inch twist. Last edited by Bart B.; October 27, 2012 at 08:06 AM.