From The Manufacturer/Wikipedia/People Smarter Than Us:
Mossberg has reinvented the classic western-style “cowboy gun” with modern touches and innovations.
Precision-machined receiver; conveniently-positioned ejection port for clearance when using optics; convenient top-tang safety; blued finished barrels in 20” length; choice of 3-dot adjustable fiber optic or adjustable rifle sights; receiver is drilled and tapped for Weaver #403 bases.