Internet myth says; "if you're getting leading you need HARD CAST bullets".
Bunk!
As has been said above, bullet fit is king. Finding out what your barrel diameter is, bore and groove diameter, then sizing you bullets accordingly, will solve most leading concerns.
Obturation is also known as "slugging up". The phenomenon is caused by inertia, the nature of an object to stay at rest unless acted upon by an outside source of energy. Basically, the rear of a bullet starts moving before the front does, when the powder pressure acts on it. This causes the bullet to slump, or change shape to a shorter shape. It also expands sideways to fill the barrel grooves.
In solid barrels like 45 acp, and 9mm, the size of the barrel determines the sized bullets final diameter. BUT in revolvers, the size of the cylinder throats, is also important. They are seldom all the same size, they should be reamed to match. That's if they are not already bigger than groove diameter. If they are, then you should size to match the cylinder throat, then let the barrel size the bullet to what it is.
I doubt your problem is one of not hard enough lead. It may even be a problem with the lube you're using. My question is; where does the leading occur? The beginning of the barrel, or the muzzle? If at the beginning or throat of the barrel, then you have a bullet fit problem. If it's more towards the muzzle, then you have a lube problem. One way to find out is to get some
Lee
Liquid
Alox. Size and lube as you have been, then tumble them in
LLA, shoot some to see if it's solved the problem.