WHAT DOES FEDERAL POWERSHOK 12 GAUGE FOR SALE MEAN?

The 590A1 is the only mossberg that is definitely mil-spec. It's current issue IIRC. Challenging to defeat, and I do not individual 1. I would be ready to guess that 870s have the degree of recognition in Law Enforcement which they do partly due to 'Keep to the chief' and partly mainly because mil-spec usually charges extra. That will influence LEO