Thread: Barrel Temp
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Old January 8, 2019, 08:55 AM   #4
Rimfire5
Senior Member
 
Join Date: January 2, 2009
Location: Northern Virginia
Posts: 705
I find that really cold barrels and hot barrels do effect POI on some of my most accurate rifles.
Seems that I get my best accuracy with barrel temps between 70 and under 120 degrees.
I mounted temperature strips on all of my target barrels so I know how fast the barrel temp is rising.
On cold days in the 20s, I can shoot 10 to 12 rounds before the barrel strip reads 120 degrees. When it is in the low 90s, I can shoot 5.
I let the barrel cool when it gets close to 120 degrees because I find that the POI is dropping about 1/4 inch as it reaches 120 degrees.
When you can shoot 0.28 groups like you do, a drop of 0.25 can double your group size.

The temp strips aren't calibrated so the numbers I reference here may not be the actual core barrel temperature, but the temp strip readings appear to be consistent and that is good enough to let me know when to let the barrel cool. I got the strips 10 for $12 from Amazon (I use the 86 to 140 deg. F. versions).

I agree with NoSecondBest that powders are also temperature sensitive, but if the bullets sitting are on the bench, the powder temperature doesn't change enough while you are shooting a group so the group size will not be effected. Outside temperature normally changes only a few degrees per hour during stable weather conditions in Northern VA, unless, of course, a front comes through.

However, temperature will change velocity by from 1.2 to 1.7 fps per deg. F. depending upon the powder. Aberdeen Proving Grounds did a study of .308 powder with extreme temperature variations. The biggest impact most will notice would be if you test a load in the early fall at 70 degrees and you go hunting in 20 degree temps on a late fall morning. That kind of temperature change could create a significant change in velocity, perhaps 60 to 85 fps for that kind of temperature difference depending upon powder sensitivity.

A deer wouldn't notice the difference but a bullet's POI might drop a bit lower than you had experienced during the summer.
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