Question for the experts, compensating a load for colder fall temps

[Road_Clam]

So back in june I was shooting 168 smk's with 41.9 gr of W748. I was measuring an average of 2560 fps and at the time the temps were about 80F. I would like to know is there any general math to compensate for the cooler 65F temps that I have currently with respect to altering the powder charge ? I'm loading up the same load only bumping the powder to 42.1 gr. I have not tested this particular load yet, so just curious how it will work. Your thoughts ??

 

[leadbullet]

keep your load the same, adjust your dope for different temp and write it down. That is way more simpler than trying to figure out how much powder to use for a given temp and you'll pull your hair out rather quickly.
easier yet, switch to a non temp sensitive powder if you can find some.
hope this helps,
cheers.

 

[jkonzal]

leadbullet is right. However, even "non temp sensitive powder" will have slightly different MV's with temp changes. As he said, just adjust your dope for the changes.

 

[HodgdonExtreme]

+1 on leaving load alone.

Bring your chrono each time you hit the range and clock 5 rounds.
Log the temperature and velocity. Develop a characteristic curve of velocity vs. Temp.
Calculate the fps per degree value (you'll have to do a best fit curve because this won't be exactly linear)
Input that value into your ballistic calculator.
Have great, trustworthy trajectory data!