Re: .338 ai f/l sizing die
"I have built and are using a 338ai on a weatherby action and after a couple of neck sizing sessions are having trouble opening the bolt even though the loads arnt excessive so now want to try a full length size..."
Do I understand correctly that you had a custom wildcat made up without having any sizer die?
Cost? Well, welcome to the wonderful world of wildcats! Since there are no firm standards for such cartridges the dimensions can vary several thousanths in any direction.
That means you SHOULD get the custom dies made to match your fired cases, not just some less expensive generic .338AI dies someone else may turn out.