Gunsmithing Stiller tac300 mag opening mod???l

[Dshooter]

Has anyone opened up the mag well on a stiller tac 300? Can or should it be done. Building a 300 ultra and seating 215 & 230 Bergers long. I think stock opening is actually close to 3.650 or so but I'm looking to go around the 3.900 according to powder fill and ogive measurements. I understand I can throat it short but as most know, it will limit powder. I know the predator actions are opened up a little bit (.130) but it's not quite enough. On that same token also looking to do the same on a rem700 s/a for my .308 but not near as much. Thanks for any help or advice