Gunpowder Variables
By Tom Wilson

All shooters engaged in reloading ammunition have been advised in articles and reloading manuals to be cautious regarding variations from lot to lot in gunpowder of the same brand and designation. This brings to mind the question of just what are the variables we can expect. Exactly what are the measurable variations in canister powder lot to lot? When your current supply of your favorite powder is depleted how much difference can you encounter in the next container you purchase? This experiment involved comparing 4 separate lots of Hodgdon Varget powder loaded into .308 Winchester cartridges. The reader must be aware that the data presenter here applies only to the samples tested. Other brands and lots of powder will certainly have different results.

First, a comparison of weight variation in a fixed volume of powder. Please be aware these samples were not loaded into cartridges. These results were determined by throwing ten charges from each of the four lots using a Lee Perfect Powder Measure. Lee states, “A soft elastomer wiper strikes off the metering chamber rather than cut the powder.” This measurer has proved to be quite reliable in throwing charges with little variation.

For simplicity each gunpowder lot number has been identified with the designation of 1-4 as shown. Below are the averages produced by this volumetric/weight comparison.

The above results from 40 charges thrown show an extreme spread of only .79 grain, less than 1%. It is felt this is quite close considering all charges were dispensed from a powder measurer. It was interesting to note the maximum spread in weight for any one lot of powder was .8 Grs.

In all firing tests close attention was given for signs of excess pressure: none appeared. If a pressure problem would have been detected testing would have been stopped with the remaining loads returned to the shop, bullets pulled and powder dumped. For ease of identification each cartridge case was marked with a permanent ink pen showing the lot number and powder charge.

Each powder lot tested began with 39.5 grains and progressed to 45.0 grains of Varget. Hodgdon lists 46 grains of this powder as the maximum load with the 168 Gr. Sierra Matchking bullet used. These bullets have always proven to be superbly accurate. Remington # 9 1/2 large rifle primers were used throughout. A Remington 700 BDL rifle re-fitted with a 26 inch Rock Creek barrel was used. The .308 Winchester chamber was set up tight but to SAAMI standards, allowing use of commercial ammunition. Gunsmithing was performed by Predator Custom Shop in Knoxville, TN; they tuned the action, and did an outstanding job. This rifle has always demonstrated very good accuracy. Twelve - three shot groups were fired from each powder lot. Chronograph screens were set up 10 feet from the muzzle. All cartridge brass used was matched to be within 1-grain tolerance.

In evaluating the four lots tested it was interesting to note the top loads of 45.0 grains of Varget recorded an extreme spread of only 26 fps. By comparison the lightest load of 39.5 Grains varied 97 fps. In comparing the 4 lots tested it indicates more consistent velocity with heavier loads. Please note the data shown in this article is not to be considered reloading data because it is not. These loads shown appeared to be safe in the rifle used for these tests. These tests reveal there are definitely differences in powder lot to lot, which can not be ignored. It should not need to be repeated; however, for those individuals new to reloading follow the practice of using reliable published data shown in reloading manuals. Always start at least ten percent below the maximum load shown and work up cautiously using your components in your firearm. However, never drop down below the minimum recommended load. Be certain to familiarize yourself with pressure signs and if they appear back down. If you run into a problem and do not know the answer almost every manufacture of reloading components and equipment have people on staff that are ready and willing to guide you: don’t guess, call them. A very wise man once said “Read the instructions and follow the rules.” This advice is an absolute when reloading ammunition.

This article first appeared in SmallArmsReview.com on June 7, 2013


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