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Ackley Improved
01-24-2008, 09:57 AM
QUESTION:

Talking PPC here, if I developed a load let say using 28.7grain of powder at 82fahrenheit, and the temperature at a competition went to either 70 or 95 fahrenheit, whats a rough value for adjusting powder weight to the new conditions?

Is 10 degrees fahrenheit worth 0.3grains roughly for example?

Cheers
AI

Gene Beggs
01-24-2008, 12:56 PM
A. I.,

Before I began using tuners, I tuned only with the powder charge once seating depth was established. Over a period of several years of analyzing data, I found that with the 6ppc and either 8208 or N133, I had to adjust the charge one percent for each FIVE degree F change in temperature. This was with sporter class rifles and 22 inch barrels. I use a Jones measure with a Culver type insert and this formula worked to be one half click (half a number) on my measure.

Once a base line is determined or in other words you have your rifle in tune at a specific temperature, make a note of the weight of the charge, the setting on the measure, i.e., 54 clicks or 53.5 or whatever and temperature. For example, say your rifle dialed in with 28.7 grains of N133 at a temp of 70F and 54 clicks on the measure. If temp goes up to 75 degrees, reduce the charge by one half click, or 53.5 on the measure.

This is the formula I used at the NBRSA Nationals in Phoenix 2003 to win the Heavy Varmint Grand. During those days, I was using light loads of 8208 behind Cecil Tucker's #3 flat base bullet. For the last match of the day at two hundred yards, the formula called for 26.9 grains of 8208. That last group measured .228. :eek: :cool:

So,,, don't let anyone tell you that light loads won't shoot and that my formula will not work. Since that time I have developed the tuner described in previous posts, which makes it unnecessary to change the load. I never change the load, tuning only with the tuner. Works gooooood! :D

Later,,

Gene Beggs