Likely the variation in published load is as stated above from different sources, also some revolvers over the years had different lengths of cylinders and longer rounds will not let the cylinder rotate. An example is the 170gr Keith swc in some .38 it has to be seated short and crimped on the driving band.
With a black hawk you will not have a length issue. But keep in mind the shorter the OAL with a given power charge the higher the pressure, the blackhawk is a very strong handgun and there are published loads in some manuals for blackhawks ONLY very stout loads.