Success
Heated up my casting furnace and topped it up with stick on wheel weights. Had about 1/4 pot full of coww in there already. So about 25/75 mix and they are releasing.
They are a dog to get off still, have to use the mold as a clamp and really pull.
I'm very happy, seems the alloy has everything to do with the release of the slug.
I'm hoping it will get easier as the mold seasons a bit. Maybe some more polishing and clean up the inside of the base pin.
Longbow perhaps I'll get you to give me a hand lapping it or touch it up with one of your reamers.
A big thanks to everyone who helped me out