Sterling SMG muzzle tip

This is the muzzle tip from a WWII British Sterling sub-machine gun. The diameters have been scaled, but it appears surprisingly accurate. Yes, the cylinders are supposed to be off center. :-)
I've been designing a number of NERF barrel accessories, and the diameters on this model have been scaled so that a regular NERF dart will fit through the middle, and so that the outer diameter matches a cylinder that fits the outer diameter of certain NERF blaster barrels.
This model is for a te