Guys,

How much impact will the weather have when doing load testing at 200 yards in mid 30s weather? Should I just wait until it warms up a little? I've got ammo to shoot so I can definitely just go shoot and delay the load testing.

Thanks,

Mel

If I am testing when it's this cold out, I make sure I am using a Hodgdon extreme or Alliant powder pro powder. It will help minimize any temp issues. Also, keep your ammo warm in the truck or in a cooler with a hand warmer in it to keep it warm. When it's this cold out, I do not load to the rifles' max pressure. If I get any pressure signs, I know to back it down some, or use the next accuracy node down. In the summer time when ammo gets hot, it will be a hotter load then. Otherwise, shoot away!

If shooting longer ranges, it will effect your trajectory, but that's an easy calculation to know with a program.

good info Chad

I read this post when it was new, and I thought to myself "I don't think it matters much with my loads". Shortly thereafter a couple of the college kids I play tennis with showed up to do some shooting. We started with the 223 and I let them shoot first. Groups were good, but they were about 3/4 inches low. Hmmm. Then we went to the 260 and it was Ok, but it had been adjusted for cold weather recently. Then on to the 270, which I had recently shot back when the weather was in the high 60's. It had been dead on. In the cold weather of yesterday, it was 1/2 inch low. Powders were: 223, H335; 260 IMR4064; 270, H4831. All low groups were directly below the warmer weather POI and not left or right at all. Hmmmm.

Obviously, that's why I missed the coyote yesterday. Had to be. Couldn't have been poor shooting. Dang coyote was coming right at me, out about 200 yards. Tried to hit him in the top of the head, but instead burned a groove down his right side. He got more air than Michael Jordon and hit the ground doing Mach 3. Well....maybe it was poor shooting.

Loads run slower in cold weather. Bullets have air that is more dense in cold weather.

And this is more evidence to the reason to document POI after (at least) recording temperature.

Thanks guys! Great stuff!



Other than bullet drop groups should still reflect accuracy of round?

Run it over a chronograph in cold weather, keep notes, and check again in hot weather.

This information allows for a calculation to adjust velocity in some ballistic programs.

0.8 fps/degree Fahrenheit is typical for the RL powders from my testing.

The Hodgdon powders vary with temperature as well despite the "Extreme" label. How much depends on the load, but 0.4 - 0.6 fps/degree F is not unusual.

RL22 is extremely temperature in my experience, and why I quit using any of the Alliant Reloder powders. The new Pro Powder is supposed to be better as Chad mentioned, but I've not tried it.

For safety, I work up to max in July and August when temps are over 100 F. If it is safe then, it will be safe year round. The converse is not true.

Then I check velocities again when temps are around 70, and then again when temps are below freezing. Odd things happen to powders above 100 and below freezing, but the only way to really find out is to go out in the freezing and burning hot temps and check them. Even Varget, which is the least temperature sensitive powder I have ever used shows change with temperatures.

In my 308 with 175's, I found Varget went from 2630 fps when over 100 F, to 2580 with temps in the low 20's. Between 45 and 90, there was minimal change. At longer distances, it begins to matter, but can be corrected if known. This load is no where near max, but it is safe, accurate, and reliable year round, as well as safe, accurate, and reliable in every 308 in which I've ever tried it.

I differ from Chad, for whom I have much respect, in that in freezing temps, I want the ammo to be out on the bench with the box open and let it freeze and shoot it through a frozen barrel to see what is really going to happen in field conditions. Similarly, in August, I let the rifle and ammo come up to ambient temperature to make sure it is safe, but I do not let it bake in the sun. I've heard/read, that commercial manufacturers test their loads for safety up to 140 F. Personally, I've been hunting for pigs in South Texas with the temp at 112 F, so ammo safety is a factor to take into account.

Accuracy/size of groups will depend on how good the load was to start with. If the "node" allowed for some variance in powder weights, say 0.5 grain of spread, then the accuracy probably will be fine. Again, the only way to know is go out and test it.

Also, because of safety concerns, I never push loads to max other than doing an initial ladder test. After that, my final load will be at least 1.0 grain below max, or else I look for another load. Also, the lower level load allows for small errors on the scale without any safety problems.

The testing in different temps then really reveals whether the load is a good one, which is not very sensitive.