NONE really. ALL 2400 loads are approximately twice the grain weight of UNIQUE at just about the same pressures, plus or minus depending upon the variables. BUT, for 300gr bullets in the 44COLT I'd use 2400. And on the other hand , of what earthly use are 300gr projectiles over the standard 45COLT bullet weight of 250, preferably the Keith 454424SWC bullet at 1050fps from the old time load of 18.5GRS of 2400 ? The answer is none.
And so it goes...