Stick ons are mostly pure lead, while clip ons (if lead and not steel or zinc) are lead, tin, antimony alloy, which is harder and more desirable for higher velocity loads.
You want the most common type of shotgun slug, the "Foster Type" to "bump up" to bore diameter for greater accuracy out of a smoothbore, so it needs to be a softer alloy.
There's nothing wrong with you blending them, you alloy will be somewhat softer, but it really isn't a problem unless you are wanting really hard bullets. Those come with their own set of problems
Personally, I'd go with a bit softer alloy any day and adjust my velocities to match because it's all about bullet placement.
JMHO.
Ed
"Not in an open forum, where truth has less value than opinions, where all opinions are equally welcome regardless of their origins, rationale, inanity, or truth, where opinions are neither of equal value nor decisive." Ken Howell
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