Colohunter wrote:Well Hoot, looks like it might be worth using CCI primers in that rifle...
Yeah, you'd think that, but they yielded the lowest velocity of the bunch and the barrel may just resonate at some frequency or harmonic thereof that the velocity agrees with. That's the theory behind OCW and OBT. I haven't run the algorithm to see what the next period is that corresponds to the next accuracy node upward in velocity. For what you can expect from a .308 caliber in a 20 inch barrel for that bullet weight, I'd wager somewhere around 200 fps faster than the 2622 fps average I got using the CCI primers will yield another sweet spot. The other three primers were almost exactly the same average velocity, though only 20-22 fps faster than the CCIs. That difference may have been great enough to move them slightly beyond the slower speed sweet spot, but nowhere near the next faster one.
That's a simplified explanation of one of the phenomena that correlate to accuracy, but certainly not the only one. About the time you think you have a handle on these factors, that's about the time an exception jumps up and bites you in the butt. The powder I was using may simply prefer a cooler primer in this caliber. Almost all of ATK's recipes for that powder are based upon the Federal 210, which is probably closer to the 210M than the CCI 200 in temperature. That's probably because they own Federal. Why promote your competition's primers?
So, the accuracy node may be there for the other three primers if I drop a few tenths of a grain in my powder charge to slow the bullet down to the speed the CCI 200 primers yielded. FWIW, their BR2 and BR4 are cooler than other Match/BR primers also. More to come from my next trip, though my obligations are beginning to stack up as the end to casual shooting weather looms closer every day. I'm supposed to be accurizing a Rem 700 for a co-worker, working up a 30-06 load using Speer 165 DeepCurls and H4350, work on my new toy and doing more experiments with the Barnes bullets for the 450b. The rifle range being closed for 3 weekends in a row, following some vicious hot weather has put me behind on this year's projects. Right now, the weather is near ideal, with clear skies and 70s all week, but I still work a full time job and a part time job. That and chores, car maintenance, family activities, yatta yatta, are in constant competition for my time. In a month or so, just after deer season, when the weather turns hostile until next May, I'll be climbing the walls from not being able to get my fix at the range. I'm not fond of shooting with numb fingers (Raynauds) and dressed like the Michelin Man.
Sorry for sidetracking the discussion.
Hoot