Temperature and loads

[pepperbelly]

I was thinking about something. Today when I went to the range to check some loads it was 105*. What do temps like this do to pressures and accuracy?
I noticed that my barrel would get hot after 5 rounds and take a while to cool down- relatively cool. I waited until it didn't burn my hand and was comfortable to place my hand on it.

Jim

 

[SnkBit]

Re: Temperature and loads

It was 103 here today also. My groups reflected such. I don't know if it was me being a snatch about the heat or the loads and the rifle that didn't like the heat but I was doing good to keep it inside 1.5MOA @ 100yds. Be interested to hear some responses.

 

[pepperbelly]

Re: Temperature and loads

If the heat causes groups to open up then I have found my load. I was shooting on the SH practical target. I fired 5 rounds at each black dot. The 43,5gr load put 3 into a hole not much bigger than the diameter of a single round. I then put 2 rounds into a similar small hole about 1/2" away. The distance in the 2 groups were probably all me. It was just too hot to be comfortable on the rifle.

These were shot from the bench off sandbags at 100 yards. Once I am satisfied with the load I will be shooting prone at 200 yards.

Jim

 

[samnev]

Re: Temperature and loads

I noticed in the 5th edition of Sierra's manual they lowered the loads for 223 and 308, and I sure others. I called them to find out the reason and was told there had been reports of high pressure using the old top loads when temp was high or weapons got hot and felt it prudent to change the loads.

 

[Fred_C_Dobbs]

Re: Temperature and loads

Different powders have different sensitivities to temperature change. The powders I use in varmint and hunting rifles are pretty temperamental. I've seen MV in my .204 change by more than 200 fps from a cold day to a <span style="font-style: italic">HOT</span> day, and my group's consistency went to ay-chee-double hockey sticks.

My first solution was to make specialty hot-weather loads by dropping the charge a few tenths. Now I just carry the cartridges in a small soft-side cooler with a pack of blue ice (be prepared to wipe off the sweat before you chamber the round).

I use Varget in my .308, in no small part because it's much more temperature tolerant, but I still carry my cartridges in the cooler when it's 90°+.

 

[skinnypitt]

Re: Temperature and loads

I only shoot Hodgden powders because they are much less sensitive to whether. Yesterday i shot a 1000 yd. F-class match and it was in the high 90's at least, with very high humidity. I was firing very fast strings (for me) and my rifle became extremely hot but i did not notice any problems on target other than my crappy shooting.