We are not police officers, but some of our best friends are.
We talk more about the differences between these two styles a little later. Important differences between Remington 870 Police and 870 Express shotguns. Sounds like your friend got an 870 wingmaster Magnum with a slug barrel. There were only standard Wingmasters and Magnum Wingmasters.
Increasingly, accessories and enhancements that have been proven valuable on the M16 or AR-15 platform are making their way onto tactical shotguns. Seems the 870 magnums I was around had magnum stamped on the reciever. All Remington 870's in 12 gauge use the same stock design, and they all interchange.