They'll work for RB in a smoothbore. Toss any w/w marked "ZN" or any that "clink" when dropped on concrete or have a body that sticks to a magnet. The small square adhesive weights are usually lower in antimony and tin than clip on w/w, and are softer. Try to cut them with pure lead if you can. A little tin (1-2%) is ok even in a muzzleloader alloy, as it helps fill out the mold at lower casting temperatures, or if you pot temp varies, and doesn't add much hardness.