ORIGINAL: HEAD0001
People think I am crazy but IMO humidity is the biggie in ML shooting. Followed by temperature. If you had 100 fps velocity difference, I would attribute that to relative humidity more than temperature. IMO the relative humidity changes the moisture content(due to the nature of ML propellants), this change, again IMO changes the burn rate of ML propellants. Some more than others. If you change the burn rate then you change the pressure, which obviously changes the velocity. All this affects POI, which is the biggest complaint ML shooter's have. "Why does my rifle shot here today, and three inches low and left tomorrow". I hear this all the time.
When sighting my rifle in, I do it under the worst conditions. High humidity and low temperatures. IMO this regulates the amount of powder my rifle will burn under the worst conditions(IMO under better conditions your rifle will burn more powder-hence this will change pressure). I have found my best loads match the amount of powder my barrel will burn. I get the most consistent results that way. If I do this then I take one more variable out of the game(how much powder I can burn). This leaves only one variable which is the MC of the powder.
If you notice target shooter's shoot light loads. This IMO is because they are burning all the powder. Some think they shoot lighter loads because of recoil.I do not think it is because of recoil. I am pretty sure if a target shooter could get a more accurate load from a larger powder charge, they would do it. Tom.
Makes sense about the target shooters. As for humidity affecting powder, I know that is the case, just based on hunting in wet/snowy conditions with FLs. If you get just aflake of snow in the pan, your cooked, and many times when thegun won't go off the powder is "mush". Happens frequently with FLs, especially in rain/sleet. Inlines are better, but they suffer similar problems, I think the reason theygo off is because of the hot charge of the 209 primer even with damp powder, it just won't have the power of dry powder. That is a real good idea Tom to test your load/sight in during the worst conditions. My problem is I don't have covered sight in ranges. Chap Gleason