During the previous powder shortage in the late 2000's I acquired a large quantity of Red Dot powder because it is useful in both shotgun and pistol loads and it was available. I found that a load of 4.0 grains under a Falcon Bullets (no longer in business) commercial cast 125 grain truncated cone bullet shoots well in a number of different .38 Special and .357 Magnum revolvers. Red Dot is a flake powder and does not meter well, sometimes showing a deviation of plus or minus .3 grains with the chosen 4.0 grain load. I was bothered that Red Dot metered so inconsistently through the powder measures and wondered how accuracy was affected. A test was devised to determine the effect of the inconsistency on paper.
The first step was to determine the consistency of my powder measures commonly used on progressive machines. Hand operated powder measures were not considered. The powder measures are a Lee Auto Disk, Lee Auto Drum, two RCBS Uniflows (one old and a newer one), a Hornady Lock N Load, and a Dillon. One hundred charges were weighed from each measure to an accuracy of .02 grains on my electronic balance and the result entered into a spreadsheet and then average, standard deviation, and extreme spread were calculated. In order to more accurately replicate the reloading process, one hundred fired cases were loaded into the case feeder, resized with a .38 Special resizing die with the decapping pin removed, charged with powder, removed from the press, and the powder charge weighed. The powder measure selected to reload the test ammo was the Lee Auto Disk because it was the least consistent (highest standard deviation) of the bunch.
The next step was to find a revolver that shoots the 4.0 grain Red Dot load well. Four Smith & Wesson revolvers were selected for testing, one each Model 686, Model 66, Model 65 and Model 15. Four, six shot groups were shot at 25 yards from each gun using a Ransom rest and the Model 15 was the clear winner. No special care was taken in reloading the test ammo.
Next, 192 pieces of new Starline .38 Special brass were primed with CCI500 primers using a Lee hand priming tool. Ninety-six of those cases were loaded using the powder measure and the other ninety-six cases were loaded with weighed powder charges held to plus or minus .04 grains. The weighed charges were charged with powder from the powder measure, removed from the press to adjust the powder charge, and returned to the press to complete the loading process. This ensured that all the cases mouths were expanded the same.
I wanted to be able to get an average group size for the sixteen, six shot groups as well as a single aggregate group for all ninety-six rounds. That required the use on one target as a base target and another target stapled on top of the base target that was moved every six shots to expose a clean area for the next six shot group. Walking downrange 32 times was much more time consuming that I thought it would be.
The results were surprising in that there was little difference between the measured and weighed groups. The average group size (16 groups) for the weighed rounds was 1.59 inches while the average for the measured charges was 1.64 inches. The aggregate of 96 shots was 2.84 inches for the weighed rounds and 2.94 inches for the measured rounds. Smallest and largest groups for the weighed rounds were .98 and 2.00 inches versus 1.23 inches and 2.12 inches for the measured rounds. Velocity was measured but the data lost due to replacement of the hard drive on my laptop. I suspect that if the test had been conducted at 100 yards instead of 25 yards the results would not have been nearly as close.
I still weigh charges that are at or near max but measure almost everything else.
Gus Youmans