Mind you, these are blended powders. Burn rate of powders vary by lot, even though the manufacturer is trying to make each lot the same as the last. The powder manufacturing process is so variable that I have heard claims that lots vary around 20% about a mean. That is why some lots of military surplus IMR 4895 seem to burn as slow as IMR 4064 or as fast as IMR 3031. For us, the powder company blends fast and slow lots, and I was told by Accurate Arms the industry standard is 10% variation from the mean for blended powders.
So what this means is that reloading manuals will have different pressures for the same charge weights of H-38 and W231 if they used cans that were from different blended lots. Another issue, and one the public does not have data , it turns out that pressures vary quite a bit given the same powder charge. I have seen information on the 3 sigma and it is eye opening to find just how much pressures vary. Given a naturally wide standard deviation, lets say 5,000 psia, and given a small sample size, lets say ten rounds, the average pressure of ten shots can vary quite a bit, which would make one think there is something different between test results, when the differences between the averages is something you would expect from randomness.
What I find is funny is how for decades our “experts” the gunwriters have been making canyons out of the small differences between powders. As an example, I have an article by Ken Waters, from Handloader I think, and he was testing powders and bullets for the 45 ACP. He says in the article that due to the poor performance he got from W231 he gave up on the powder, just awful stuff, but HP-38, that was one of the best for low to medium pressure loads. Since now we know that both powders were identical, how did he find any difference between the two?
Was his condemnation of W231 due to lack of free samples from Winchester?, or can’t Ken shoot straight between magazine changes?
And why are these “experts” considered “infallible ” by the shooting community?
