Measure your throats, if they're too small your bullet will not be filling the grooves and gas will blow by, alternatively if they're too big the gas will blow by the bullet and soften the lead by the time it has entered the bore.
The worst leading I've had so far is with the Taurus Judge and that's due to the giant .456 throats that my .452 bullets don't care for.
I've had issues with Speer lead projectiles in the past, I think that's more the dry lube that's used and that cleans out the bore after I shoot jacketed or plated bullets.
My experiences with Ruger is they like to run their throats big with the magnums, but on the Super Redhawk that makes no sense for them to do that.
Then again with the way Ruger is these days I shouldn't be surprised.