Busted!!! Turn them in. Sure it wasn't Utah?

Another thought is they could have been using a ML during an any-weapon season - to pimp one of their sponsors ML's. Then a scope could be used.

From the 2017 Regs:

3. MUZZLELOADING RIFLES
& SMOOTHBORE MUSKETS
a. Only legal muzzleloaders allowed in muzzleloading seasons.
b. In-line muzzleloaders are legal.
c. Must be a single barrel that fires a single round ball or conical projectile.
d. To hunt deer, pronghorn or bear, they must be a minimum of .40
caliber.
e. To hunt elk or moose, they must be a minimum of .50 caliber.
f. From .40 caliber to .50 caliber, bullets must weigh a minimum of 170
grains.
g. If greater than .50 caliber, bullets must weigh a minimum of 210
grains.
h. Shotshell primers and B.O.R. Lock MZ System bullets are legal.
i. Pelletized powder systems are prohibited during muzzleloading
seasons.
j. Cannot be loaded from the breech during muzzleloading seasons.
k. Only open or iron sights allowed in muzzleloading seasons. Fiber optics
and fluorescent paint incorporated into or on open or iron sights
are legal. Scopes or any sighting device using artificial light, batteries
and electronic gear are prohibited during muzzleloading seasons.