Michigan requires my AR rifle to be transported in the trunk Funny because I can carry an AR15 pistol in the passenger compartment under my CCW permit. Therez not 25 cents difference in the guns in my estimation. Go figure!
This is largely why, IMHO, the AR15 “pistols” became popular. Even in states that allow long guns to be accessible inside the passenger compartment of motor vehicles, many states/jurisdictions require that such rifles and shotguns be kept unloaded. Some such laws and regulations are found in the fish and game laws/rules, if not in the actual penal/criminal codes. Yet, in many of these places/situations, any handgun can be kept loaded.
Of course, the concealed-handgun-license “movement,” that occurred in the Eighties and Nineties, is what enabled widespread legal carry of handguns, so it had to happen, first. I could not legally carry a handgun until 1984, when sworn as an LEO. My “bag gun,” up to that point, had been an Uzi Carbine, with the collapsible stock option, and Texas law allowed me to keep it loaded. (Texas law remains quite long-gun friendly; just be careful of the few prohibited places for ALL firearms, and, of course, places where federal law applies.)
To this day, there are places/situations where one cannot legally carry a handgun, even with a carry permit/license, but long guns can be discreetly and legally carried. (The legal particulars are probably best further discussed in a different thread, in the Legal section of THR.) Because of this, it makes sense, to me, to have an AR15 pistol, and also an AR15 carbine with a minimal-length folding or collapsible stock, in order to be able to “rule book” various combinations of laws, with one weapon system, with the same ammo, same magazines, and same/similar manual-of-arms. (Actually, at the moment, my AR15 pistol is 300 AAC/BLK, so it does not match my .223/5.56 carbines, but I plan to remedy that next week, with another upper, when funds land in my checking account.)
Interestingly, I am not a “fan” of the AR15/M4. It is simply a matter of practicality, and the system system having originally been chosen for me, if I wanted to carry a patrol rifle, while on duty, back in my LEO-ing days.