Question. For you guys whose got more experience in reloading than me. I have a remington M7 7mm08. Getting ready to reload for. I bought some hornady SST 139 grain bullets and some 140 grain NBT. I want to know if 1 grain different between the two bullets really make a difference in the powder charge. I know that the books say YES! but has anyone used say, said powder charge like 4064 powder charge for the 140 nbt for the sst 139. I had to ask. I understand that 1/10 of a grain can make a Bev difference in accuracy. So please don't. Judge my question as ignorant. Sometimes you just have to be schooled. Thank you I welcome all replies.
I think the thickness of the bullet jacket, hardness of jacket, and the hardness of the core have more an influence towards increasing/decreasing pressure than one grain difference in bullet weight. This has to do with how much force it takes to swage the bullet through the throat and then into the rifling. Of course, knowing the jacket thickness, and hardness of either the core or jacket is something you can't investigate with home tools.
In terms of accuracy, I believe that location of the center of gravity has a much greater affect on accuracy than slight weight differences. And then, just how good of a shot are you and is your rifle a bench rest rifle? If your weapon requires you to hold it, but the butt in your shoulder, and use your hand to pull the trigger, than sight alignment, stock weld, and trigger pull errors are magnitudes greater than tiny weight or charge differences. The in print press is all about equipment, emphasizing that such mundane things as practice are unimportant to shooting compared with expensive equipment and gadgets. I don't know if any bowls anymore, but the most perfect, round bowling ball will go right into the gutter, just as a bad ball, if you don't know how to roll it at the pins.
I have shot excellent scores with thrown charges of IMR 4895, short grained stick powders that throw about plus or minus 1/2. I tested thrown IMR 4064 in a 30-06 and that shot well, that powder is probably a plus or minus a grain.
Barrels tightness makes a huge impact on pressures. My Douglas barrels and Wilson barrels in 223, I had to cut loads by 1.5 grains to avoid blown primers in a Kreiger barrel.
There are differences in pressures between bullets, my suggestion is to start with midrange loads and see how they do. Don't try max with new bullets, and, the more you shoot them, don't be surprised if you find that you need to reduce the loads later.