woah...lots of factors involved but you can get a basic idea
for black powder the combustion gas temp is 3307 degrees
you have to divide this number by a constant (R)
the constant for black powder is 22.16 per foot
or 1.846 per inch
so if you wanted to know the(theoretical) temp say 6" from the charge you would multiply 6(inches) X 1.846....=11.076
divide the combustion gas temp 3307 by 11.076...
= 298 degrees,,but you would have to factor in the volume of the chamber,diameter of charge ...ect .but you can be sure that the temp will be no higher than these calculations
hope this helps some