Gatsby-

Look Here

450-

That tool is essentially what I'd have suggested, but I didn't expect you to have the access and aptitude in the tool room!
Excuse the assumption.

I'll look back in my posting history and dig up a couple of photos of the hand tools and process that I use to load for my bore rifles.
The tooling is stone simple.
Do you have a lathe in the engineering shop?

Also, have you considered using Goex 2f powder?
It's such an elegant solution to the powder question in this kind of loading. Best feature of all is that it cleans with cold tap water, no chemicals - and you can rinse and re-use your cleaning patches and mops.
If only for kicks and giggles you owe it to yourself to give it a try, it actually simplifies the process.

Cheers
Tinker