This morning I went to the range to play with a couple of rifles. My Ruger 77 in .25-06 and my Model 10 in .308. Working up loads for the Ruger, I loaded two different bullets with the same powder charge. The 117 grain Hornady SST and the 117 Sierra Gameking. I loaded them both with Reloder 19 and Reloder 22 powder.
So, I Loaded the same brass with the same primer and powder and seated two different bullets. The first load was 46.0 grains of Reloder 19, half seated with the Hornady, half seated with the Sierra.
Then I loaded another series with the same brass and primer, but used 50.0 grains of Reloder 22. Half seated with the Hornady and half seated with the Sierra.
Then I pushed them over the chronograph. For reasons I haven't divined yet, the Hornady bullets flew faster than the Sierra with both powders.
117 Hornady, 46.0 RL19, 2728 fps
117 Sierra, 46.0 RL19, 2667 fps
117 Hornady, 50.0 RL22, 2870 fps
117 Sierra, 50.0 RL22, 2797 fps.
Who'd have thought that changing the bullet would change the velocity by that amount? Not the weight of the bullet, but the brand? That's the beauty of this hobby; you learn something new every time you go out, and just about the time you think you know what you're doing, you find something new that makes you scratch your head.