Thanks again for the input.
I think I learned something today and if anyone has any knowledge or experience with what I'm talking about, please let me know.
I loaded 4 different charges of Magpro and the Berger 140 VLD. I started at 72 gr. and ended up at 73.5. I chronographed all loads and here are the results:
Temp: 22, Elev: 6300:, adjusted barometric pressure: 23.9, humidity: 15%.
All loads chronographed between 3288 and 3309 and accuracy was about the same with everything. They all shot 1.5 in. or better at 200 yds.
My conclusions are:
1. This powder is sensitive to temperature and has a max. burn rate regardless of the charge when it's cold. I'll bet I don't get the same results when it's 80 and I don't see this with extruded powder.
2. I have reached the max that the barrel can burn and here again, regardless of the charge, everything that doesn't burn is simply thrown out on the snow.
Now, I'm not a scientist and don't have any technical training but these are the only two scenarios that I can come up with that would explain the consistency of the velocities regardless of the amount of powder used.
I laddered up a load with H4831SC and saw an increase in velocity with each increase in charge.... the same with IMR4831. Even though the charge weight was different, the best accuracy was attained between 3380 fps. and 3410 fps. At those velocities in the 26 1/2 in. barrel both produced groups of .75 or less at 200 yards. That, by the way, is probably as good as I can shoot at that range under those conditions.
If any of you with some technical knowledge can add some light to what I have described it would be appreciated. Even though I've been doing this quite a while, I'm still learning..... especially when it comes to long range dynamics and I'm open to comment or suggestion.