If one increases the case capacity by 10%... what is the rule of thumb for the increase in powder charge?
If you increase net case capacity by 10%, you can put in about 10% more powder. The trick is knowing
which powder will keep you within the pressure limit. The only thing known is the new burn rate must be somewhat "slower."
If for some odd reason you want to keep the same powder in both the parent and the blown out case, that's a different problem. Lee's first edition reloading book had a table of approximations one could use to estimate this, at least for single base powders -- I don't have my notes at hand; sorry. QuickLOAD will give you an approximation, too. You might compare the maximums in a load book for the .300 H&H and the .300 Wea for a given powder and bullet weight. Hodgdon's data isn't helpful, though: It shows the smaller case outperforming the bigger one when using 220 gn bullets.
