First try is a failure, i need to be able to center the sizing ring.
I’m going to find someone local who can thread the sizing ring so that i can screw it into my RCBS Cowboy 12ga die. Then i should be fine

There are no failures, just experience in gaining knowledge about what works and what doesn’t.
Yeah true.
Just heard back from a mate who says his brother inlaw is a fitter and turner at a local sugar mill.
Says hes a shooter aswell, hopefully catch up soon and get him to do it.
What thread are you chasing??
Find out the what thread in your press is and see if you can get hold of a grade 8 -10 bolt that will screw into it. Then just bore it out to suit. Use plenty of sizing lube on your brass and I reckon it’ll work. I’ve made firing pins out of grade 8 bolts for some antiques and they last pretty well. If you cant find a thread to suit you’ll have to get it cut. My old lathe only has change gears for Whitworth. (I did say it was old)
Met with the bloke this morning and explained what I’m trying to do, he has the cowboy die and the 16ga sizing ring.
He seems pretty enthusiastic to have a shot of it when i get it loaded up.
Got my die back, updates tomorrow when i finish crying about the football.
You crying about Collingwood??
Yeah mate!
Now we’re getting somewhere!