I'd be nervous about the "combat" reliability of a semi-auto.
Wonder why??is our military gone from autos to trap doors again?I believe if you did your P.M. on it and kept her clean she would serve you well.
as for the mossberg being a military shotgun being issued.You must remember that today the lowest bidder makes your gear.
I don't ever recall the military useing the 870s,but I could be wrong.all I have ever seen was ithcas,winchesters and mossberg.the do have some full auto shotguns that the sf and sog use.But they are not normal looking shotguns.and as for which shotgun is better?870 or 500 or 590..I really like the 870s,they serve me well and a couple are the 1st made,never had to replace parts on them cept fer a stock are a forearm,our club (Trap)had several club guns in 870.they were shot a lot.very rarely cleaned cept ta wipe the outside down.they just kept on shootin.just hold the barrel up push the slide relase and the forearm would fall down, now that is a used pump gun..one of my 870s that I used for years huntin in the jungles never let me down.rain all over it mud and crud all over it,swimin cross rivers with it ,god only knows what fell in the barrel while trudgen thru the jungles and balstin a deer are pig with her.and besides that,I think they look more pleasin then some of the other pump guns,cept for the win M-12s,but they were complex and to me required a little more P.M. then the 870s..