The 281 alloy melts at too low a temp to fully cure the powder. The quote below is from Kurt Urban at CS Coatings:
"Powder paint needs a minimum of about 275º to achieve the chemical cross-linking for a complete cure." If you're on BassResource.com search for my post, "Six Degrees of Separation."
I'm now casting Rotometal's Lead-Free Bullet Casting Alloy with good results.
https://www.rotometals.com/lead-free-bullet-casting-alloy-88-bismuth-12-tin/
I cure the powder at 325º for an hour in Eastwood's oven. As an aside, I'll mention that if you purchase this large capacity, made-for-powder-paint oven, spend an additional five bucks and buy an oven thermometer - the dial temp on my oven is off 50º!
After this curing procedure the jig heads easily pass my "whack on vise" test.
To avoid muttering and cursing, liberally apply Drop Out mold release. It's available from barlowstackle.com. Bismuth expands as it cools.
The 88/12 alloy is hard enough so you can grip the casting in the middle - not the sprue, not the hook shank - to remove without marring it.
So, if you need to fish lead-free as I do in Massachusetts, go with the 88/12 alloy or pewter (at even greater expense and lighter weight).