42 .If manual says 42grain in 243 or 308 how mutch minimum at least i load the charge?
if you load less than that, you are increasing the air in the case. This causes pressure spikes. If the powder is too low, you will explode the rifle.
Before the armchair ninjas pounce , let me say that if you want to, or do have have air in your rifle cases, please just go on quietly and spare the debate.
It's my policy to have little to no air in a rifle case. Dacron is your friend. For example, 1 grain of dacron fills my 500 Jeffery case when I use 100 grains of IMR 4166.
Weigh the dacron on an electronic scale. In a 308, 0.5 grains of dacron goes far. If you shake a loaded round, ideally you should not hear the powder rattling.
So if you want to go under 42, fill the space with dacron. Dacron is the polyester fluff in cushions and pillows. Ask your wife nicely for an old one.