Burn rate,does NOT translate to muzzle velocity "gains". One does not "gain" velocity,in a burning rate shift that is faster,when reducing a barrel's length.
Few are a greater fan of modest barrel lengths than I,but Physics is ALWAYS Physics. Hint.
Rather than fixate a velocity,I'd look at uniformity(ES/SD),as that constant will pay more in downrange favors. I've long been a fan of increased propellant densities(slower burning rates),to yield that very thing. If ES/SD are in check,temp swings are "doable"...then ALL else will assuredly follow suit.
Source some Alpha brass(uniformity is OFF the fucking charts),dump Re-15 into the hole and bask in the sanctity of mechanical excellence.
Just sayin'.