Now, let me share an experience I've had.

Last fall I worked up a load of 2.5 gr. Unique in .38 Special cases under a 205 gr. bullet. This was to be used in a .357 Maximum rifle for small game. It would group into 1-1.5 inches and about 2 inches low of point of aim at 50 yards (sights set for the full-throttle deer load). At 25 yards they were spot on. I could see using these for a wide variety of small game including ground hogs, fox and "others" of that size. I loaded 50 to have to use and tested part of that batch to make certain I had it right. All was well. However, I had never chronographed that load. I did use one round to take one squirrel (on the ground).

Well, today I took it with me when I went shooting the Max (testing Lil'Gun loads). VERY disappointing! What happened! Well today (temp 59 degrees, similar to when I worked up the load) velocities went from 83 fps (yes, not a typo) to 340 fps. Most were striking 2 feet low at 50 yards (but 3 were spot on! ). These loads were useless today.

About midway through the test it occurred to me that they had been stored bullet down in the box and maybe the powder was not next to the primer. All following rounds (18) were given a sharp (but safe) rap on the bench before firing and the rifle barrel was elevated immediately before firing. Little if any improvement. Indeed, I did get a good group, just 2 feet too low! The 3 that were right on were from the first 22 rounds...

I don't know what happened here but I'm going to try a few more and see what happens...