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Rimfire5 · January 8, 2019, 04:39 PM

Unclenick,

The article cites that primer types, barrel temperature, and powder temperature can be variables when considering the results of temperature change and that all three need to be considered. I was quite impressed with the article and found that the author's findings agree with observations made during my less formal experiments.

Without having read his initial suggestions, I realized quite some time ago that I needed to keep the variables he cites as constant as I could in order to focus on the outside temperature variations when shooting for accuracy.

1) In my approach to achieve accuracy with my most accurate rifles and attempting to keep the bullet exit time to match the reflection time of the barrel steel, I always use the same primers for each caliber (choosing primers based on testing of different primers with the same loads to determine which yields the best accuracy). The primers are not a variable. 1a) By the way, I have tested using magnum primers versus regular primers on my .30-06 hunting rifles in 23 degree cold temperatures and measured a 12 fps increase with the magnum primers versus regular primers using my chronograph. I think that is in the range of increase that the article indicates. It isn't enormous but there is a slight increase.

2) I have temperature strips (86 to 140 deg. F.) on my all match rifle barrels and monitor barrel temperature when shooting groups to ensure that the barrel temperature doesn't climb more than 5 degrees for any group. I also have documented that my best rifles' POIs drop by between 0.25 and 0.35 inches depending on the caliber when temperatures of the barrels climb to around 122 degrees. I generally stop shooting and allow the barrels to cool at 110 degrees before the POI drops and then start my groups over at 86 degrees. Once I start shooting a group, I don't waste time letting a cartridge get hot sitting in a hot barrel, as the author recommends.

3) My results with Hodgdon's 'Extreme Powders' (particularly H4895, IMR4166 and IMR4451), like the author observes, indicates that the velocity does appear to change with temperature regardless of what Hodgdon claims. I had thought that the adjustments I was making using QuickLOAD to match temperature forecasts were working because I was getting group average results at 35 degrees that were as good or better than the results I was seeing at 70 degrees early this Fall with charges matched for that temperature. Of course the powder charges were slightly smaller in the warmer temperature, sometimes by tenths of a grain. What I have determined is that all these powders are lightly less temperature sensitive to changes below 70 degrees than they appear to be at temperatures above 70 degrees. The curves aren't perfectly linear but are near enough to consider them linear. Aberdeen Proving Grounds data also shows the velocity changes are not quite linear.

4) I had also noted in the table that the smaller calibers seem to be more sensitive to temperature. The author also makes that observation.

You picked an excellent article to reference. It is a keeper.

January 8, 2019, 04:39 PM	#12
Rimfire5 Senior Member Join Date: January 2, 2009 Location: Northern Virginia Posts: 923	Unclenick, The article cites that primer types, barrel temperature, and powder temperature can be variables when considering the results of temperature change and that all three need to be considered. I was quite impressed with the article and found that the author's findings agree with observations made during my less formal experiments. Without having read his initial suggestions, I realized quite some time ago that I needed to keep the variables he cites as constant as I could in order to focus on the outside temperature variations when shooting for accuracy. 1) In my approach to achieve accuracy with my most accurate rifles and attempting to keep the bullet exit time to match the reflection time of the barrel steel, I always use the same primers for each caliber (choosing primers based on testing of different primers with the same loads to determine which yields the best accuracy). The primers are not a variable. 1a) By the way, I have tested using magnum primers versus regular primers on my .30-06 hunting rifles in 23 degree cold temperatures and measured a 12 fps increase with the magnum primers versus regular primers using my chronograph. I think that is in the range of increase that the article indicates. It isn't enormous but there is a slight increase. 2) I have temperature strips (86 to 140 deg. F.) on my all match rifle barrels and monitor barrel temperature when shooting groups to ensure that the barrel temperature doesn't climb more than 5 degrees for any group. I also have documented that my best rifles' POIs drop by between 0.25 and 0.35 inches depending on the caliber when temperatures of the barrels climb to around 122 degrees. I generally stop shooting and allow the barrels to cool at 110 degrees before the POI drops and then start my groups over at 86 degrees. Once I start shooting a group, I don't waste time letting a cartridge get hot sitting in a hot barrel, as the author recommends. 3) My results with Hodgdon's 'Extreme Powders' (particularly H4895, IMR4166 and IMR4451), like the author observes, indicates that the velocity does appear to change with temperature regardless of what Hodgdon claims. I had thought that the adjustments I was making using QuickLOAD to match temperature forecasts were working because I was getting group average results at 35 degrees that were as good or better than the results I was seeing at 70 degrees early this Fall with charges matched for that temperature. Of course the powder charges were slightly smaller in the warmer temperature, sometimes by tenths of a grain. What I have determined is that all these powders are lightly less temperature sensitive to changes below 70 degrees than they appear to be at temperatures above 70 degrees. The curves aren't perfectly linear but are near enough to consider them linear. Aberdeen Proving Grounds data also shows the velocity changes are not quite linear. 4) I had also noted in the table that the smaller calibers seem to be more sensitive to temperature. The author also makes that observation. You picked an excellent article to reference. It is a keeper.