At lower velocity, and corresponding lower pressure, you need a softer bullet that will slug up to fit the chamber throats and bore perfectly.
A too hard bullet at plinking pressure will likely cause gas blow-by and leading.
http://missouribullet.com/technical.php The standard Hardball Bullet Casting Alloy consists of 2% tin, 6% antimony and 92% lead. With a .430" diameter. Its a good place to start with 8 to 10 gr of Unique for a "plinking" load. I have no idea what my scrap alloy is, but its hard.At the Missouri Bullet Company, we optimize bullets for your intended application. We don't take a “one size fits all” approach to manufacturing your bullets. We work with certified analysis foundry alloy in two hardnesses in order to provide you with the bullet hardness that works best for you. One is 2% tin, 6% antimony, balance lead for harder bullets at 18 BHN and the other is 1.3% tin, 4% antimony, balance lead. While it is expensive for us to maintain a dual supply of alloy, the payoff is in the fact that we can offer you a choice of bullet hardness.
Yes.
I've been loading 44 hard cast bullets for years in several 44's loaded from very mild to full house loads and have never got any leading.
If they're sized to .430" you'll be fine.
Shooting cast bullets is not the problem some on the internet make it out to be.