Hardcast I looked at the burn rate chart. I did load the slower 3031 with 2 more grains and good golly did it give me a thump on the shoulder compared to the 4064 charge. The 50 gr of 4064 was pleasant to shoot but the 52 gr of 3031 put 2 black and blue marks on my shoulder. That Marlin Cowboy doesn't have a recoil pad, just a solid plastic butt plate.
I just might try and drop the 4064 charge down one grain and also up one grain from 50 grs and see what happens.