Updated: Aug 12, 2020
Shooting started for me at a young age in western Pennsylvania. When I turned 18 I joined the Marine Corps and became a Scout Sniper. This is when my passion for shooting really took off and I began reloading and learning more on my own. Throughout my time of shooting and reloading, I have read, seen, and experienced a number of issues with modern commercial propellants. When I first started reloading, I constantly heard people discussing what powders were temperature sensitive and which ones were not. This article applies to almost everyone in the shooting community because it's important to know how your ammunition will function in different atmospheric conditions. If you prefer factory ammunition this test can easily be done to see how well your load performs in different climates.
When I became a sniper in the Marine Corps we learned that for every temperature rise and fall we had a correlation in the change of our D.O.P.E.S(Data on previous engagement this is simply the adjustments recorded from the scope to hit a certain distance). We needed to track these changes for an accurate firing solution to engage targets. Because of this need, we are constantly hounded to keep our ammunition out of the sun so that our ammunition was as consistent as possible.
The purpose of this article isn't to promote one product over another but instead to highlight the differences from powder to powder. Some would even say the sample size is too small to show any real results, however I have found that my samples did yield results. I chose three different powder loads just to show that it doesn't matter what powder or factory ammunition you are running, atmospheric conditions still have a measurable effect. These swings in muzzle velocities can change your point of aim, point of impact and cause the standard deviation of your load to increase. This means that at distant targets you may actually miss high or low depending on how the conditions are affecting the ammunition. The term we will be using to discuss these changes is standard deviation. Standard deviation is something you could easily write a whole article on by itself. Precision rifle blog gives a great example about standard deviation “If you had a standard deviation of 10 fps for your muzzle velocity, that means 68% of your bullets would exit the muzzle within 10 fps of the average velocity. That is + or – 10 fps, so if your average muzzle velocity was 3,000 fps, then you could expect 68% of your shots to be between 2990 and 3010 fps. (The whole article can be read here on the precision rifle blog).
I contacted custom ammunition manufacturer, Unknown Munitions and asked them to load three different test loads. For this test I will be shooting the Remington .223 cartridge using the 77gr Nosler RDF bullet, Hornady brass and CCI 450 primers. The key difference between the loads was the brand of powder. In an attempt to keep bias out of my test, I asked them to not label which powder was used in the subsequent load. What I received was load “#1”, “#2” and #3”, I was not notified of the powder in each load until testing was completed. All cartridges were loaded to a COAL of 2.42” and fired from a 26” barrel, bolt action rifle. None of the loads were developed for my rifle, they are generic loads that Unknown Munitions chose.
Temperature: 80 Fahrenheit
Station Pressure: 24.72 inhg
Elevation: 5178 Feet
-Ambient loads were allowed to sit under my truck in the shade. The average temperature for these rounds was 86 Fahrenheit.
-Cold loads were frozen the night before in a freezer and put into a cooler until right before firing. The average temperature for these rounds was 22 Fahrenheit.
-Hot loads were left on the hood of my truck in mid day heat. The average temperature for these rounds was 133 Fahrenheit.
-All temperatures were recorded with a laser thermometer, LaserGRIP 1080 Infrared Thermometer
-Muzzle velocities were recorded with a LabRadar chronograph
-Atmospheric conditions were collected from a Kestrel 5700
-The barrel was cleaned in between the different loads and 3 fouler rounds were fired to give each load the best chance at performing.
--Perform these tests at your own risk--
--Warning these loads are safe for my rifle--
--Warning if you are reloading and know that you are near max pressure I do not recommend performing this test--
Load #1: 77 Nosler RDF seated at 2.42 C.O.A.L, CCI 450 Primer, Hornady 223 casing, Powder IMR 8208 XBR
Load #2: 77 Nosler RDF seated at 2.42 C.O.A.L, CCI 450 Primer, Hornady 223 casing, Powder Varget
Load #3: 77 Nosler RDF seated at 2.42 C.O.A.L, CCI 450 Primer, Hornady 223 casing, Powder RL-15 Below are the results: