Does anyone shoot a 500 with the Lyman #501680 cast bullet
(375 gr.) using 12.5 grs. of Unique without any leading? The Lyman 49th loading manual says this will be 1065 fps. Got a new 500 (8 & 3/8) and I don't want to lead plate the barrel first thing. I will be using straight wheelweights. Thanks

I have no Lyman molds

However I push my hard cast 400 grain semi pointed .500 projectiles past 1800 fps without a leading issue.

Presuming your projectiles fit your bore, your straight wheel weights should be good for velocities much higher than you are planning.

Make sure you use a good lube.

If you find problems, there are many solutions.

I water quench my projectiles for additional hardness.

You can use gas checks made from soda cans on PB bullets. You can buy a check maker for about $80 or $90 or just purchase pre-cut ones off the internet.

Or you can forget about lube altogether and powder coat the projectiles.

Any or all of these will get you to 1800+ FPS territory

Been using Lyman Range Magic Premium lube in a Redhawk with good results. That's a 240 gr. ww lead with 10grs. Unique.
Never a sign of leading. Just don't want to mess up a new gun with leading.

I push those to just 1200 FPS without leading, pretty good bullet. I use unique as well, slightly higher charge which I cannot recall.