May 17th, 2018

Powder Temp Stability — IMR Enduron vs. H4350 and Varget

powder gunpowder temperature sensivity temp stability Hodgdon Extreme Varget H4350 IMR Enduron 4451 4166

A couple seasons back, (PRB) published a significant field test of powder temperature stability. The test was designed to quantify the temperature stability of Hodgdon H4350 and Varget powders compared to IMR’s Enduron line of powders, specifically IMR 4166 and 4451. The results were very interesting, to say the least…

Hodgdon Extreme Series powders have attracted quite a fan base, with over 90% of the top shooters in the Precision Rifle Series choosing to run one of those powders. IMR offers a modern line of powders “with Enduron Technology” — which is also marketed to have “extreme temperature stability”. Sounds familiar! These new powders should compete directly with the Hodgdon Extreme Series, which gives shooters more temp-stable powder options to consider.

CLICK HERE to Read Full Powder Temperature Stability Test on Precision

The top shooters in the PRS and veteran long-range shooters in other disciplines have learned to value a temperature-stable powder. That’s because a change in temperature can affect the trajectory or “flight path” of the bullet in two well-known ways:

1. Assuming all other environmental conditions remain the same, an increase in air temperature will cause a flatter trajectory due to a lower air density (easier for the bullet to cut through the air).

2. The same increase in temperature also causes the nitrocellulose-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. (SEE: Temperature Effects On Zero on

“The initial heat condition of your powder will affect the burn rate,” Bryan Litz explained at a recent Applied Ballistics Seminar. That means swings in ambient outside temperature can affect your internal ballistics, which will directly affect your muzzle velocity, which will change your bullet’s trajectory. Some powders are more affected by changes in temperature than others. So if your goal is first-shot hits and you may shoot in a variety of conditions — you should care about temperature stable powders.

The folks at meticulously loaded 6.5×47 Lapua ammo with each powder using some of the best equipment available. This included the top-of-the-line Prometheus Gen II Powder Scale, which is capable of loading to the nearest kernel of powder. This ensured the powder charges were identical for each round of ammo. PRB’s testers explain the full set of equipment and steps in their loading process in the Full Test Report.

Magnetospeeed LabRadar chronograph chrono powder gunpowder temperature sensivity temp stability Hodgdon Extreme Varget H4350 IMR Enduron 4451 4166

Once they had a couple dozen rounds loaded with each powder, they went and shot them with each powder at 25° F, 65° F, and 140° F. The muzzle velocity of each shot was recorded using BOTH a LabRadar Doppler Radar and a MagnetoSpeed Chronograph. That provided two sets of velocity numbers. When placed and configured optimally, the LabRadar can measure muzzle velocity with +/- 0.1% accuracy, according to the manufacturer.

Here are the results from the PRB Powder Temp Stability Tests:

Magnetospeeed LabRadar chronograph chrono powder gunpowder temperature sensivity temp stability Hodgdon Extreme Varget H4350 IMR Enduron 4451 4166

You can see Hodgdon H4350 had the least variance in muzzle velocity, with just 25 fps over the 115° swing in temperature! That is very, very low. Hodgdon Varget was the second least temperature sensitive powder in this test, with 46 fps of variance in muzzle velocity between temperatures of 25° F and 140° F. IMR 4166 performed very similar to Varget, and proved to be fairly insensitive to large swings in temperature. IMR 4451 had the largest swing in muzzle velocity of the powders tested, but keep in mind just 68 fps over 115° F swing is still a good performance.

Most powders aren’t specially formulated to be temperature stable. So they would likely show much larger swings than what these four top-performing powders showed. However, Alliant’s relatively new Reloder 16 is an extremely temp-stable powder, with a burn rate that is a close match to H4350. Many F-Open competitors are now using Reloder 16 with considerable success.

PRB’s test team also noticed other interesting trends in the data. For example, variation in velocity does NOT appear to be linear across the full range of temperatures. By that, they mean the change per degree from 20° to 65° might be smaller or larger than the change per degree from 65° to 140°.

PRB’s testers talk about those things, provide a few other insightful views of the data, and discuss tools that can help you manage temp/muzzle velocity in the field in their full post. You can find that here:

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