I am shooting a 284 shehane and 183 sierras. My powder charge and seating depth range have been developed at 1000.
Powder has been measured to the kernel(calibrated a&d scale), brass weight sorted, brass annealed, cases sized equally, cases trimmed,bullets sorted by weight/ogive, br2 primers and seated with a hydro press. I've gone over the typical things such as scope, bedding, rings, base, rear bag, front rest, etc and nothing is loose. The barrel is a 4 groove krieger with roughly 320 rds thru it.
The shift in vertical I am seeing at 1000 yards coincides with my increase in velocity. I know I am within the powder charge node and a good seating depth because groups are good and vertical is good if I separate the two distinct velocities I am measuring with my labradar.
The issue I had today started with 5 rds using s&b primers and 54.9gns of h4831SC. My velocity was in the 2820-2830 range (higher velocity than what previous testing yielded)and vertical at 1000 was less than 6". In previous testing my charge yielded 2740fps. I adjust my scope to move the group from the 7-8ring on a 1000 yard fclass target down to the X ring.
After the first 5 rds with S&B primers I shifted to my usual br2's. The rounds were now running 2750 fps and impacting 20" low on target. I adjust scope again and end up hammering the 10 and X ring with less than 6" of vertical. Not sure how a primer would cause an 80-90fps swing in velocity because I have used these primers before and found that they usually don't vary more than 10fps if any.
Suddenly, my velocity shifted up to the 2810-2830 range and the rounds formed a nice group between the 7-8 ring. The shift in velocity measured by the labradar coincides with my drop chart. 80-90 fps meant roughly 20" high on target!
I am using fully prepped lapua brass that I have successfully used in the past and I have not been able to detect any mechanical or Mother Nature factors that could cause this. The rifle shot excellent at 2750 or 2830 but when will it make up its mind and stick to one or the other?
If any of you have any ideas or suggestions I am open to your words of wisdom.... My next test is to not clean the barrel and try 15rds with s&b primers and another 15rds with br2's to see if it hovers between two distinct velocities.
Thanks.
Powder has been measured to the kernel(calibrated a&d scale), brass weight sorted, brass annealed, cases sized equally, cases trimmed,bullets sorted by weight/ogive, br2 primers and seated with a hydro press. I've gone over the typical things such as scope, bedding, rings, base, rear bag, front rest, etc and nothing is loose. The barrel is a 4 groove krieger with roughly 320 rds thru it.
The shift in vertical I am seeing at 1000 yards coincides with my increase in velocity. I know I am within the powder charge node and a good seating depth because groups are good and vertical is good if I separate the two distinct velocities I am measuring with my labradar.
The issue I had today started with 5 rds using s&b primers and 54.9gns of h4831SC. My velocity was in the 2820-2830 range (higher velocity than what previous testing yielded)and vertical at 1000 was less than 6". In previous testing my charge yielded 2740fps. I adjust my scope to move the group from the 7-8ring on a 1000 yard fclass target down to the X ring.
After the first 5 rds with S&B primers I shifted to my usual br2's. The rounds were now running 2750 fps and impacting 20" low on target. I adjust scope again and end up hammering the 10 and X ring with less than 6" of vertical. Not sure how a primer would cause an 80-90fps swing in velocity because I have used these primers before and found that they usually don't vary more than 10fps if any.
Suddenly, my velocity shifted up to the 2810-2830 range and the rounds formed a nice group between the 7-8 ring. The shift in velocity measured by the labradar coincides with my drop chart. 80-90 fps meant roughly 20" high on target!
I am using fully prepped lapua brass that I have successfully used in the past and I have not been able to detect any mechanical or Mother Nature factors that could cause this. The rifle shot excellent at 2750 or 2830 but when will it make up its mind and stick to one or the other?
If any of you have any ideas or suggestions I am open to your words of wisdom.... My next test is to not clean the barrel and try 15rds with s&b primers and another 15rds with br2's to see if it hovers between two distinct velocities.
Thanks.