![]() ![]() The speed increase of the round brought on by higher temperatures typically lags the increase of the speed of sound brought on by the same higher temperatures. That said it appears from my limited research that I wont have issues with regard to staying below the speed of sound developing loads in the winter and shooting them in the summer. So, Accurate's site would indicate, don't worry about it while Hogdon's would crack the door to concern with some (very limited?) powders. It also stands to reason that they found the most extreme temp sensitive powders for comparison as it makes their powder look better. And while these FPS differences would effect accuracy/distance it appears only one powder of their limited list would make a difference in the potential to go supersonic shot on a hot day if loaded to be on the edge of subsonic on a cold day. On Hogdon's site referencing "extreme powders" they compare a limited number of powders in different cal's and loads to theirs. Therefore most shooters do not notice much difference under normal practical hunting conditions." 5% of a 1000fps load over this temp range is only 50 fps vs 181 fps for the speed of sound range over the same temp range so basically, not an issue to worry about. However, we test at -40F and +125F and the deviation in most cases are ca 3% to 5% at these extreme levels. Its a bit crazy finding information but on the Accurate website they do state "Most of our powders are not insensitive, and will show some effect at hot and cold temperatures. So what powders would be equal to or less than this delta over these temperatures? speed of sound on a -40 degree day = 1004, and on a 125 degree day its = 1185. So for our extremes shooting purposes we'd likely operate within the following range. The density of the air has no effect, because the ratio of the air pressure to the density is always constant. I've learned, (somewhat contrary to what a lot of people run with), that the speed of sound is the same on a mountain top as it is at sea level if the air temperature is the same. ![]() What I'm trying to learn is, while using my powder(s) Accurate 1680, Hogden CFE BLK, and VV N120, will the speed change (increase) by shooting a cartridge that's 40 degrees vs one that's 100 degrees equal more than the FPS increase in the speed of sound over the same temperature increase. The last thing I want to do is load up a 1000 rounds that will be supersonic in the summer!!!Īll other ballistics aside apart from being subsonic below the speed of sound. I've found an accuracy and speed node but it's not too far from going supersonic (50 fps +/-). As I'm working up different subsonic loads for bulk reloading I'm beginning to wonder how much of a speed increase may occur if I develop/test a load in 40 degree weather and then shoot it on a 100 degree day.
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