Your rifles need to have the receivers pillar bedded, the forearm bedded, and the barrel free floated. It is the inconsistant or irrattic contact and pressure of the stock and barrel that is causing your problems, not your loads. Your best load is your best load. Only extreme changes in weather conditions would cause loads to be suspect. But let the humidity get extremely high or extremely low for a couple days, or let the rifle(s) get wet, then you will have problems. The only way to eliminate that problem is to pillar bed the receiver, bed the forearm, and free float the barrel. I have shot enough benchrest competition to know that a good accurate load, will remain accurate over a wide temperature range, say 50 degress + or - 20 to 30 degrees. Some powders tend to be more stable over a wider range of temps than others, so some loads developement may require hot versuses cold weather testing.