Lead/Cu builds up near the forcing cone. That is a very rough barrel with horrible tool marks. I would contact Colt.
I never really considered my Python to be more accurate than similar revolvers from other makers; What impresses me is the slick/smooth as glass working of the action. The competitors had nothing to compare with it unless you spent $$$$ to have your revolver tuned and smoothed... Glad I got (and kept) my old Python- doubt if the new Pythons will be as good or as valued in 30 years...The original Pythons barrel bores were slightly tapered to increase accuracy.
Here's an interesting article about the Python and the details of what went into making one.
"A second reason for the legendary Python accuracy is the barrel.
Samuel Colt and his employees actually invented high precision, high production barrel rifling machinery in the 1840's. This type of barrel rifling machinery and process changed very little until the 1950's.
Colt was one of the few American gun makers to manufacture their own barrels, and Colt barrels were always famous for their quality and accuracy.
Colt went even farther with the Python barrel. It was manufactured to an even higher standard with an ultra-smooth bore and a faster rifling twist that stabilizes the bullet better.
Uniquely, the Python bore was tapered slightly toward the muzzle.
As the bullet passed down the barrel the tapered bore gripped the bullet tighter, increasing accuracy.
As part of the manufacturing process, the Python barrel was given a somewhat mysterious treatment known as "the silver ball".
In this process a silver colored ball of a secret material was pressed down the bore with a hand press device. This left the inside of the barrel very uniform, perfectly smooth, and with a brilliant mirror-like shine.
All of this combined to make the Python capable of astounding accuracy.
A number of shooters have obtained one hole, 3 shot groups at 25 yards that are smaller than a .45 caliber bullet.
More than the fine fit and finish, it was the Pythons accuracy that made it a legendary revolver."