Thickness Under Front Dovetail of Rifle

[Cosmoline]

I recently installed a standard patridge style sight in the custom barre of a Winchester big bore. At the thinnest point it has reduced the barrel thickness from .150 to .050 under the middle of the dovetail cut. This is only a little bit shy of the crown. I am now concerned I may have taken too much. The chambering is .450 Marlin.

Does anyone know what the rule is for under-dovetail rifle barrel thickness?