Rol_P said that it was fun "watching Dan stuck on success". What is fun for Roland is driving me crazy.
Over time, I have observed that with the 140 & 150 gr. bullets that when the velocities get above 2950 fps the accuracy greatly degrades. The best observed accuracy with these heavier bullets have been in the 2900 to 2950 fps range.
I shot the first target below on 4-12-15. It was with a 140 BT with 55.5 gr. of IMR 4831. It looked very promising. Dr. Mike ran a couple of QL projections for me and I thought I golden to zero in on an OBT of 1.2282 milliseconds by dropping back 1/2 grain of powder. Everything suggested I would achieve a velocity of about 2915 fps.
Instead the exact same load yielded the second target with an average velocity of 2977 fps. The reduced load of 55.0 gr. of IMR 48331 yielded an average velocity of 2938 fps - nearly where I was two weeks ago with 55.5 gr. of powder.
I don't understand what variable confounded me. The temperature on 4-12-15 was about 70 degrees F whereas the temperature yesterday was about 46 degrees F. The case weights on 4-12-15 were from 178.0 to 178.4 gr. The case weights yesterday were from 177.5 to 177.9 gr. I was expecting my velocity to go down based on those two things.
There are two minor differences I didn't take into account. The cases I used yesterday were resized one more time - resized a total of three time. The cases I used on 4-12-15 had been resized only two times. Can resizing (work hardening) a case make the velocity 30 fps faster?
Before I shot the cartridges on 4-12-15 I tweaked some to ensure good concentricity. However, I didn't mark the ones I adjusted and no way of knowing which, if any, of the shots on the first target were adjusted. All of the cartridges I loaded yesterday morning had concentricity variances of less than .003" so I didn't adjust any of them. Could concentricity adjustments on 4-12-15 changed the average velocity downward?
Any thoughts on this would be appreciated.
Dan
Over time, I have observed that with the 140 & 150 gr. bullets that when the velocities get above 2950 fps the accuracy greatly degrades. The best observed accuracy with these heavier bullets have been in the 2900 to 2950 fps range.
I shot the first target below on 4-12-15. It was with a 140 BT with 55.5 gr. of IMR 4831. It looked very promising. Dr. Mike ran a couple of QL projections for me and I thought I golden to zero in on an OBT of 1.2282 milliseconds by dropping back 1/2 grain of powder. Everything suggested I would achieve a velocity of about 2915 fps.
Instead the exact same load yielded the second target with an average velocity of 2977 fps. The reduced load of 55.0 gr. of IMR 48331 yielded an average velocity of 2938 fps - nearly where I was two weeks ago with 55.5 gr. of powder.
I don't understand what variable confounded me. The temperature on 4-12-15 was about 70 degrees F whereas the temperature yesterday was about 46 degrees F. The case weights on 4-12-15 were from 178.0 to 178.4 gr. The case weights yesterday were from 177.5 to 177.9 gr. I was expecting my velocity to go down based on those two things.
There are two minor differences I didn't take into account. The cases I used yesterday were resized one more time - resized a total of three time. The cases I used on 4-12-15 had been resized only two times. Can resizing (work hardening) a case make the velocity 30 fps faster?
Before I shot the cartridges on 4-12-15 I tweaked some to ensure good concentricity. However, I didn't mark the ones I adjusted and no way of knowing which, if any, of the shots on the first target were adjusted. All of the cartridges I loaded yesterday morning had concentricity variances of less than .003" so I didn't adjust any of them. Could concentricity adjustments on 4-12-15 changed the average velocity downward?
Any thoughts on this would be appreciated.
Dan
