Some folks fire muzzleloaders without eye protection: This is not a good thing, especially when the gun does not have a closed breech.

This old pair of eyeglasses with glass lenses was shot using a .177 air rifle at five feet. The gun was given one pump and fired at the left lense. This was repeated for the other lense. Neither lense broke. Neither lense broke when the gun was given two pumps. The lense finally broke when the gun was given three pumps.

A pair of glasses will protect the eyes from about anything that could come out of a muzzleloder except for the bolt or a big chunk of the breech. Polycarbonate lenses are even stronger.