All shotguns have the same gun ability if you have at least a +1 bonus with it:
You have advantage on attack rolls against creatures with medium or heavy armor.
KSG : 50 Gold
1d10 Piercing + Str/Dex, 20ft Range
(1 Shots Until Reload)
Mossberg 590 : 85 Gold
1d12 Piercing + Str/Dex, 30ft Range
(1 Shots Until Reload)
UTS-15 : 105 Gold
1d20 Piercing + Str/Dex, 50ft Range
(2 Shots Until Reload)