Unique has been successfully used with lead bullets for over 100 years.
Re: leading in revolver—
You have to know the throat diameters of your cylinder—you will want bullet diameter to be no more than 0.0005" smaller than the smallest throat diameter. You should be able to just barely push a bullet through the throat.
Is the forcing cone smooth or rough. This is the surface that the bullet crashes into and goes into a plastic-flow situation. If it is rough, it will initiate leading.
You have to know the groove-to-groove diameter of your barrel. Your bullet should be somewhere around 0.001-0.004" larger than the groove diameter for best accuracy.
Cast bullet revolver accuracy is more dependent on throat-bullet fit than any other factor, assuming other good loading practices. The reason is that undersized lead bullets are subject to gas cutting, which will positively ruin their accuracy potential. Most of the gas cutting takes place while the bullet is in the throat. When it hits the forcing cone, it will obturate if it is large enough.
You may very well find that your bullets shoot better with no
sizing at all. My bullet lubrisizer was retired about 20+ years ago.
In a revolver the throats are the areas in each cylinder chamber
immediately ahead of the portion of the chamber where the brass case rests and into which the bullet projects. If the bullet is sized so that it is a gentle force fit in the throat, all else
being equal, your accuracy potential will increase greatly.
Two factors come into play here to improve potential accuracy:
a) the bullet axis is more nearly coaxial with the barrel axis.
b) gas cutting, which will positively RUIN accuracy, is virtually
eliminated.
I have never seen any observable pressure increases when using bullets up to .006" over groove diameter and I have seen no increase in accuracy using sized bullets.