Why temperature sensitivity matters in reloading

November 10, 2019

Why temperature sensitivity matters in reloading

Varget vs Shooters World Precision

What's up Reloaders! We've been asked to compare Varget and Shooters World Precision powder.

These two powders are incredibly similar. So, we broke the testing down to the most important aspect of gun powder, temperature sensitivity. Both of these powders are marketed as being temperature stable, but which one comes out on top?

To perform this test, we've used the following components for a .223 build from Brownells.

Why temperature sensitivity matters in reloading

Upper Receiver

Vortex Razor HD Gen II 4.5-27x56MM FFP H59
American Defense Recon QD Mount
Cross Machine Tool Ambidextrous Match Receiver Set
Aero Precision Upper Parts Kit
Spikes Tactical Nickel Boron BCG
Power Custom Steel Charging Handle
18" White Oak Armament 223 Wylde Match Barrel
Geissele MK4 Super Modular Rail
Seekins Precision Adjustable Gas Block
Spikes Tactical Rifle Length Gas Tube
Dead Air Armament- Sandman Keymount Brake
S-BRM Harris Bipod
Cerakoting Republic Rifle God's Plaid

Lower Receiver

Cross Machine Tool Ambidextrous Match Receiver Set
Geissele Lower Parts Kit
Geissele .154" SSA-E Trigger
Ergo Grips Suregrip
Magpul PMAG 20 Round Gen M3
JP Enterprises Silent Captured Spring Gen 2 H2 w/ Alt Spring Pack
Luth-AR Brownells Stock Kit
Cerakoting Republic Rifle God's Plaid

Now, let's get down to it.

Why temperature sensitivity matters in reloading

Why does temperature sensitivity matter?

If you’ve never read up on the effect temperature can have on reloading, here’s a brief look, and then we’ll jump into the details.

"A change in temperature can affect the trajectory or ‘flight path’ of the bullet in two well-known ways:

So long as altitude, barometric pressure, and humidity remain constant, an increase in air temperature will cause a flatter trajectory due to a lower air density (less collisions with ‘air particles’ per unit length of flight path).

The same increase in temperature also causes the nitro cellulose-based powder inside the cartridge to burn at a higher rate, producing approximately four times the Point of Impact (POI) shift than just air temperature alone.

Just how much does an increase in temperature affect the powder burning-rate? Some powders are more susceptible to temperature effects than others and will burn faster than others."

- Kestrel Meters, “Temperature Effects on Zero"

Now that you understand why temperature sensitivity matters, put yourself in this scenario for a second. You walk up to the range in the wintertime after just working up some unreal hand-loads earlier that summer. You sit down, get ready, and start sending them. You look downrange and your impacts aren't hitting in the same spot, or you flat out missed your target.

Why's that? Well, due to differences in temperatures and other variables, your trajectory will change, specifically, your muzzle velocity. I know, I know, one more thing to think about when making ammo. But that’s why temperature-stable powders are a must when reloading for everyday conditions.

Think about it. If you’re shooting in the morning with 50-60-degree weather, then later on in the day as it warms up to 70,80, or 90 degrees, you can start to see a major difference in muzzle velocity. Also, if you aren't a reloader and just shoot factory ammo, bad news: This applies to you as well.

Before we started this temperature test, we warmed up with 10 rounds. The next 5 shot strings were fired within one minute, and in between those strings was a barrel cool down period of 10 minutes. Each round was loaded with identical components, weight sorted by lot, annealed, concentricity checked along with using L.E. Wilson hand dies, and measured to the 0.02 grain of desired powder weight.

For the powder charges, Precision takes a little less powder than Varget to achieve the same velocities. As a result, we worked up a load specifically to match the same FPS to give a fair and accurate representation of both powders. Moreover, filling both cases to the same amount of powder would give two widely different results that would give misleading readings.

To make this test the most realistic, we took the following steps to replicate weather conditions from 30 to 100 degrees Fahrenheit. We first conducted the heat portion of the test by using a sous vide cooker. The idea was presented by Ken Johnson, in which we placed 5 rounds and waited till they reached exactly 100 degrees. From there, we removed the bullets from the cooker and immediately went straight to firing them downrange with the Magnetospeed Sporter. We purposely fired them right away because we did not want them to vary in temperature from the outside elements, in order to give the most accurate representation.

After that, we then removed the other bullets from the freezer, which came in at exactly 30 degrees and were also fired. The outside conditions are as follows: pressure was 29.93", humidity 76%, elevation 1050 feet, 65 degrees Fahrenheit.

Why temperature sensitivity matters in reloading

Why temperature sensitivity matters in reloading

Why temperature sensitivity matters in reloading

Why temperature sensitivity matters in reloading

In retrospect, these numbers jumping around 60-70 FPS is pretty solid for both powders being temp stable. You should also remember this is coming out of an 18" barrel with safe loads. We were chasing the best groups and not the most FPS. Your results can vary on several different factors. However, this is within the ballpark based on what you will find conducting your tests.

Grouping comparison

I figured I’d also share my groupings during my load development. However, I am a pretty decent shooter, I'm sure most of you guys with this rifle could be achieving same shot, same hole. With all the gnats flying into my eyes and into my ears, I got off some pretty decent 5 shot groups.

Now, for this test, we also intentionally used once-fired brass. If you’re curious why, brand new brass tends to be near the minimum specs. As a result, hand-loads in new cases would most likely have more pressure than a once-fired, resized casing, giving us false and misleading readings in our load development.

For the following, we used a L.E. Wilson full length bushing die along with the L.E. Wilson seating hand die and arbor press. We shot 5 round groups from 100 yards with our Brownells build. We found that 77 Sierra Match Kings with Jagermann brass and CCI Small Rifle Primers seated .005" below case head, shot out of a White Oak 18" .223 Wylde barrel with a 1/7 twist worked best.

The weather conditions when the tests were performed are as follows: pressure was 29.93", humidity 76%, elevation 1050 feet, 65 degrees Fahrenheit on October 5th, 2019.

  • Varget:
  • 1st group: 0.432"
  • 2nd group: 0.567"
  • 3rd group: 0.589"
  • 4th group: 0.423"
  • 5th group: 0.486"
  • Average MOA: 0.4994"
  • Precision:
  • 1st group: 0.366"
  • 2nd group: 0.456"
  • 3rd group: 0.390"
  • 4th group: 0.375"
  • 5th group: 0.429"
  • Average MOA: 0.4032"

Final thoughts

Varget and Precision are both extremely temperature stable powders. In the future, I will personally continue to use both. However, I will say Varget tends to fly off the shelf. Precision is a great and cheaper alternative to have in your toolbox if you don't have a bunch of Varget laying around. I highly recommend you give it a shot. Pun intended.

As always, shoot straight, be safe, and happy reloading!

To read the full version of this blog, and to check out tons more info on reloading, head over to Reloading All Day.

For those of you who want to get some Precision powder, here’s a code just for you at Midsouth Shooters Supply. They are one of the few sellers currently selling Precision, as you usually won’t find it in mom and pop shops yet. Use code: SWART1119 for half off hazmat.

BIO

Blake

Blake has been writing reloading articles for three years and helping out within the community to further enhance reloading education. In his free time, he works within the community to help out new hand-loaders by educating them on the many variables that come with this wonderful hobby. His passion is solely based on educating others so that they may pass on that information to future generations, keeping the art of hand-loading alive.

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