First you have to define what it is before you can decide if it is legal:
CHAPTER 1 CHAPTER 1. OF THE STATUTES.
8.3t “Firearm” defined.
Sec. 3t. The word “firearm”, except as otherwise specifically defined in the statutes, shall be construed to include any weapon from which a dangerous projectile may be propelled by using explosives, gas or air as a means of propulsion, except any smooth bore rifle or handgun designed and manufactured exclusively for propelling BB’s not exceeding .177 calibre by means of spring, gas or air.
History: Add. 1959, Act 189, Imd. Eff. July 22, 1959.
From
http://www.legislature.mi.gov/Publications/Firearms.pdfSo, by statute, it is a Firearm.
Now the question is: are firearms legal in Michigan?