Date: Jun 08 2009
Fastidious handloaders simply know their reloads will provide the most uniform velocities and the best accuracy when they use the same brand of cases. Cases of different makes can vary in internal volume up to several grains of powder, which can lead to swings in velocity. But by using all one brand of cases, and even cases from the same lot, velocity will be more constant and accuracy the best possible.
After running an experiment with two common cartridges shooting the same make of cases from the same lot and a mix of case brands with a couple of different powders, I can definitely answer seeking perfection via using the same cases may or may not be worth the bother.
The first rifle I tested was a Savage Predator Hunter .223 Remington. Barnes 40-grain Varminator bullets were used with H-4198 and W-748 powders in the same lot of Winchester cases and a mix of commercial and military cases. Each charge of powder was weighed on a scale, cases trimmed to the same length, the same primers used and all bullets seated to the same depth.
Military cases usually have thicker walls than commercial cases, which can reduce powder capacity somewhat and produce higher pressures. So when using military cases, it’s a good idea to back off maximum powder charges a grain or two. The two powders used in the .223 loads were about one grain below maximum and in the military cases showed no signs of excessive pressure. The military cases used were Lake City ’83, ’85, ’94 and ’97 for some of the .223 Remington loads listed in the table. Those cases produced most of the faster velocities, showing they had somewhat smaller internal capacities than commercial cases.
The second rifle was a Ruger MKII .30-06. The Ruger is a basic hunting rifle that on an average day groups five shots in about 1.5 inches and on a good day three shots in maybe an inch. For its loads, Berger 168-grain Match bullets were used with W-760 and IMR-4350. The Berger bullets and each powder were loaded in Hornady cases from the same box and Federal, Remington, Hornady, RWS and Winchester cases. Everything else was kept the same.
Follow along with the shooting results listed in the table.
With the Ruger .30-06 shooting Berger 168-grain bullets over 52.0 grains of W-760, there was a slightly less extreme spread of velocity with Hornady cases compared to the mixed brands of cases. The relatively high extreme spread of velocity with the Hornady and mixed cases was probably because the 52.0 grains of W-760 did not quite fill any of the cases with the bullets seated. That allowed the powder to settle any which way in the cases and on firing produce a relatively wide extreme spread of velocities.
Extreme spread of velocity is reduced substantially, though, when cases are filled with enough powder that
seating bullets slightly compresses the powder charge. That is if all the cases are the same make. Seating Berger bullets in Hornady cases slightly compressed 58.0 grains of IMR-4350. With the powder charge locked in one position in cases with the same capacity, extreme spread over five shots dropped down to a decent 19 fps. The same amount of IMR-4350 seemed to be compressed when bullets were seated in the five different brands of .30-06 cases. But the varying case capacities of the five brands still produced three times the velocity spread as cases of all the same brand and capacity.