Colt's Walker pistol was rated to handle 60 grains of Black powder with a round ball or conical bullet load. However Colt recommend it to the Army that they not use this maximum load as standard, because it would cause excessive wear on the gun--and in practice it often caused the ramrod/packing lever to come loose from under the barrel.
When the gun was loaded with the maximum acceptable powder charge it would generate about 1130 ft./s velocity, and the ball would strike with 400 foot pounds of energy (at the muzzle).
That means it was more powerful than most 115 grain 9 mm ammo and on par with 124 grain NATO spec ammo.