I own 2 Mossburg 500 shotguns. One of them makes my shoulder black and blue everytime it's fired; the other has almost no kick whatsoever. Except for the year of manufacture (12 years apart) they appear to be identical. It's the newer one that kicks.
These are both the civilian version, not the military (long shell tube) version.
The long magazine version is not limited to military or law enforcement, anyone can buy one. (YMMV by jurisdiction of course). Mossberg shows it in their online catalog.
It's just not as handy for most civilian purposes.