Michigan has nothing that is codified in MCL. The Feds have the CFR 479.11 which is what they base things on, and it IS LAW:
In that they use the word "muzzle", but have graciously included permanently attached muzzle devices into the length of the barrel. I would have to go looking for it, but they also define what constitutes "permanent"For purposes of this definition, the length of the barrel having an integral chamber(s) on a shotgun or rifle shall be determined by measuring the distance between the muzzle and the face of the bolt, breech, or breech block when closed and when the shotgun or rifle is cocked.
That was just a "whim" of AG Frank Kelley in Opinion #6820. He was trying to balance out our laws with a 30" OAL with the Federal CFR of "extreme ends" and a 26" minimum. The opinion that he came up with allowed us to own a wider range of firearms, yet still maintain the concept of an illegal SBR (at that time they were illegal in Michigan). What the Feds use is this:
Except in one of the ATF "guides" they used the word muzzle, which is not supported in law and is most likely by error of some clerk trying to make it more readable.The overall length of a weapon made from a shotgun or rifle is the distance between the extreme ends of the weapon measured along a line parallel to the center line of the bore.
There is nothing published, but several people have asked the MSP and they get a "less non-permanent attached muzzle devices" answer, which is based in law for barrel length. Yet, they apply the same process to OAL, which is different, than barrel length. Only a portion of barrel length is counted into the OAL of most firearms and should include any muzzle device, the rest is internal to what ever stock is used.
And FFL is a Federal Licensee not a goto for Michigan law, you will get as many answers as there are LEOs, Lawyers, or Representatives and Senators.