Had a charge weight that was shooting 1/2 MOA groups during load development that I did when it was around 55 degrees. The charge weight was right around where the max weight for it was listed and I had even shot .4 grains higher with no pressure signs at the time I tested everything. The velocity of the 1/2 MOA groups was right at 2670.
Since then its gotten over 100 degrees and I decided to take that rifle out and shoot and took some of the old test loads which were under the 1/2MOA optimum charge to test how temperature sensitive this powder was (IMR 4895). I'm glad I did because with even .4 grains UNDER the optimum load (1 grain under what I had tested to be completely safe in 55 degrees) had extractor marks and was very tough to pull the bolt handle. I didn't chrono this but this has me wondering, and wanting to chrono a slightly lighter charge next time.
Since the optimum charge that led to extremely high accuracy is due to an accuracy node / optimum barrel time is this as simple as finding what charge (while keeping everything else the same) will give me 2670 fps again and making a note of this for this temperature and in the winter switching back; kind of letting the temperature be the difference in powder but getting the same velocity, hence the same barrel time? Or am I going to have to start this over completely with lower loads to find it at the much higher temperature?
Since then its gotten over 100 degrees and I decided to take that rifle out and shoot and took some of the old test loads which were under the 1/2MOA optimum charge to test how temperature sensitive this powder was (IMR 4895). I'm glad I did because with even .4 grains UNDER the optimum load (1 grain under what I had tested to be completely safe in 55 degrees) had extractor marks and was very tough to pull the bolt handle. I didn't chrono this but this has me wondering, and wanting to chrono a slightly lighter charge next time.
Since the optimum charge that led to extremely high accuracy is due to an accuracy node / optimum barrel time is this as simple as finding what charge (while keeping everything else the same) will give me 2670 fps again and making a note of this for this temperature and in the winter switching back; kind of letting the temperature be the difference in powder but getting the same velocity, hence the same barrel time? Or am I going to have to start this over completely with lower loads to find it at the much higher temperature?
