Cessna flier, i was in the army. The US Military (all branches) use the mossberg 590, which mechanically is the same as the 500. But mossberg was made to upgrade most of the internal and some of the external parts (because mossberg was making the 500 with cheaper parts that were not reliable)before the contract was first agreed on.

Also I would not choose to own anything for the lone reason that the military uses it, because the government probably bought it from the lowest bidder.