13579,
Since commercial canister powders are generally tested before release to burn within 2% of a standard, it is just about impossible to adjust a load to the same velocity and result in excessive pressures--unless your old load was on the ragged edge anyway.
One basic APPROXIMATE rule of internal ballistics is that pressure increases at about twice the rate of muzzle velocity. Thus a 2% increase in velocity would develop about 4% more pressure--or increase a 60,000 psi load to 62,400.
In practice using a chronograph to adjust for differences in lots normally results in even less increase in pressure. I know
this from working in a couple of pressure labs.
