Steve is correct. Virtually all the powder in a rifle or handgun that will burn has burned in the chamber and first few inches of barrel. Some powder kernels do not burn at all, but that's not because the charge was still burning.
Optimum burn rate of powder depends on ratio of bullet sectional density to charge weight.
The heavier the bullet (all other things being equal) the slower the powder for optimal power.
However, the smartest way to find it is as mentioned. Get a couple loading manuals and see what gives good velocities. Also, when one gets reloading manuals, one finds reading the introduction about all the components and assembly very enlightening.
Just for the record, I have a Remington 700 VLS in .308 Winchester and the best load I have for it is a military surplus 174 grain match bullet and 41 grains of IMR 4895. That uses Federal cases and whatever LR primers I can find.