When transitioning from spring to summer, should I go down in my powder charge as the outdoor temperature rises? If so, how much should I drop back to start over? Does humidity play a factor in this calculation?
Last year I shot benchrest competition for the first time using my 6 BR using 28.5gr of Varget pushing a Berger 105gr Hybrid at 0.025 MOA. If I remember on hot days my bolt lift got a little harder. This year I’ll be shooting a 22 PPC using 26.0gr of H322 pushing a Berger 55gr FBHP with a 0.010” jump. This combination produced a 0.185” group at 100 yards. should I change to a powder that is more suited to warmer climates?
IF, that load in your PPC is near max and it is hot you could cross over into excess pressure territory. Still getting 0.185” groups can win many matches if it is repeatable. A change in powder could end up with you struggling to get that small a group and you might never get there. There are things you can do to keep the temperature down on your loads. Keep your rounds in the shade, better yet in a cooler in the shade. Adding a 1-2 thous jump will lower pressure, but may degrade accuracy. Be sure your current load doesn’t enlarge in the heat as it may and still not give you any pressure signs. If you can find a comparable load with a less temp sensitive powder it might be worth the hassle and experience, but it might not happen. Good luck.
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Thank for your help. As I looked back over my original post I noticed a mistake in my wording. With my 6 BR it was a 0.257” average group size not a 0.025 MOA. The gentleman who won shot a 0.241” average also with a 6 BR.
generally i have found colder temps require less powder. cold air is more dense. same with dry air. so when temps and/or humidity increase your load will be more likely to stay in tune with more powder. always look for signs of pressure in primer deformation.