I just got my .308 back from the gunsmith last week. I had welded a new handle onto a new PT&G bolt (O.D. of 0.700") and the headspacing was too short so it went to the gunsmith. He removed about 1" from the chamber end of the barrel and cut a new match chamber. He also installed a BO recoil lug. I managed to paint the barrel and bolt with GUN-KOTE (light desert tan, base color for camo pattern), installed a new BO 20MOA base and then reinstalled the scope.
This past weekend I decided to use up 23 loads that I had left over from a match back in June. That particular load shot very well at 600 yards and I considered it to be the OCW load for the original Krieger barrel and chamber. The OCW load consisted of 43.2gr of Reloder 15, a Nosler 168gr HPBT CC bullet, Lapua brass once fired and neck-sized, a CCI 200 primer and an OAL of 2.845". MV was right around 2,700 fps.
The first thing I discovered is that the new chamber is shorter than the original chamber so I had to seat the bullet 0.044" deeper to maintain 0.020" of clearance off the lands. Those cases were fired once in the original Krieger chamber and were neck-sized only so they wouldn't chamber in the new match chamber. I ran all 23 loads through a body die to bump the shoulder back to SAAMI specs. Given the required changes to the OCW load, I wasn't expecting much. After sighting in the scope, I shot one 5-shot group before the rain came and ended the day. Here it is ... 0.662" shot at 100 yards prone with a bipod. To be honest, I wasn't expecting such a good result but now I'm even more convinced of the validity of the OCW method. This weekend I'll make up 42.9gr, 43,2gr and 43.5gr to see if 43.2gr is still the OCW load for this rifle. It'll be interesting to see if the velocity increased a little with the bullet sitting 0.044" deeper in the case.
Here's the rifle ...
My thinking/understanding/interpretation re the OCW method is that the primer and powder ignition result in a shock wave that moves from the chamber to the muzzle and back again at some frequency (many times before the bullet leaves the barrel). The vibration that results is a function of the amount of powder, the energy of the primer and the mass and stiffness of the barrel and chamber. The position of the muzzle is a function of the frequency of the vibration of the barrel. The fact that the barrel and chamber are now both shorter has a minimal effect on the resonant frequency of the barrel/chamber so the OCW doesn't change even though the bullet is now seated 0.044" deeper. Case sizing, bullet seating depth, neck tension, case neck thickness, neck runout, bullet runout etc. all play a part in the group size, but it's my opinion that those variables don't affect the OCW load much at all. They simply fine tune it from good to better to best. I'm open to any thoughts on this so fire away.
This past weekend I decided to use up 23 loads that I had left over from a match back in June. That particular load shot very well at 600 yards and I considered it to be the OCW load for the original Krieger barrel and chamber. The OCW load consisted of 43.2gr of Reloder 15, a Nosler 168gr HPBT CC bullet, Lapua brass once fired and neck-sized, a CCI 200 primer and an OAL of 2.845". MV was right around 2,700 fps.
The first thing I discovered is that the new chamber is shorter than the original chamber so I had to seat the bullet 0.044" deeper to maintain 0.020" of clearance off the lands. Those cases were fired once in the original Krieger chamber and were neck-sized only so they wouldn't chamber in the new match chamber. I ran all 23 loads through a body die to bump the shoulder back to SAAMI specs. Given the required changes to the OCW load, I wasn't expecting much. After sighting in the scope, I shot one 5-shot group before the rain came and ended the day. Here it is ... 0.662" shot at 100 yards prone with a bipod. To be honest, I wasn't expecting such a good result but now I'm even more convinced of the validity of the OCW method. This weekend I'll make up 42.9gr, 43,2gr and 43.5gr to see if 43.2gr is still the OCW load for this rifle. It'll be interesting to see if the velocity increased a little with the bullet sitting 0.044" deeper in the case.
Here's the rifle ...
My thinking/understanding/interpretation re the OCW method is that the primer and powder ignition result in a shock wave that moves from the chamber to the muzzle and back again at some frequency (many times before the bullet leaves the barrel). The vibration that results is a function of the amount of powder, the energy of the primer and the mass and stiffness of the barrel and chamber. The position of the muzzle is a function of the frequency of the vibration of the barrel. The fact that the barrel and chamber are now both shorter has a minimal effect on the resonant frequency of the barrel/chamber so the OCW doesn't change even though the bullet is now seated 0.044" deeper. Case sizing, bullet seating depth, neck tension, case neck thickness, neck runout, bullet runout etc. all play a part in the group size, but it's my opinion that those variables don't affect the OCW load much at all. They simply fine tune it from good to better to best. I'm open to any thoughts on this so fire away.
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