47 Walker Colt
The Model 1847 Walker Magnum does indeed fire a 60 grain load. I own an Uberti copy and routinely fire 60 grain loads with a .457 dia round ball and a wonder wad. However, the gun shoots much more accrurately using a 50 grain charge.
If you wish I can demonstrate this via video. I use the gun extensively. Yes it is massive, far bigger than the 1860 Army 16 1/4" long with a 10" barrel and weighing in at 4 1/2 pounds.
"In 1846, Captain Samuel H. Walker, former Texas Ranger and captain of the United States Mounted Rifles, ordered 1,000 revolvers of an improved design from Samuel Colt. Tested on the battlefields of the Mexican War the formidable four pound, nine ounce Walker, with its .44-caliber bullet propelled by a heavy charge of black powder, remained the most powerful handgun until the introduction of the .357 Magnum in the 1930s." -from Uberti.com
A freind of mine chrono'd the .457 cal 90 grain roundball / 60 grain blackpowder load at 1200 fps. I personaly think 60 grains is a bit too hot so I shoot a 50 grains. I have used a 50 grain Pyrodex load with both the 90 grain roundball and the 180 grain conical which is as powerful as the blackpowder load, Pyrodex being somewhat more powerful. You should not use more than 50 grains of Pyrodex.
The weapon's Owner's Manual recommended these loads. This is in an Uberti copy... I would not reccomend even shooting an original. One sold at auction not long ago for $137,000.