I know that they are both great combat and/or defense shot guns (Military, LE, home personal protection) i am in the market for an outstanding 12ga for defense. so far there are very few differences between the two as far as effectiveness and quality goes. below i listed make/model of the two and what i know about them already.

http://www.mossberg.com/images/Mossb.../New/51772.jpg

Mossberg M590A1 (black water series)

-8+1 12ga
-3" chamber
-BBL: 20" heavy walled barrel (parkerized)
-rear sight ghost ring on rail, front sight AR style white stripe
- Tang safety, easy access for lefty or righty shooters.
-pump safety at rear of trigger guard making easy to access (apposed to remington's which is infront. bit of a reach
-tri-rail fore end
- bayonet lug
- speed feed stock +4 12ga (with a side saddle (6) the speed feed stock (4) and a 9 capacity weapon would be carrying 19 shells alone on the fire arm, making it one heavy bitch but seeing how ammo, capacity and reloading time with shotties, a benefit?
-drilled and tapped receiver for rails and optics on ALL m590a1
-metal trigger, trigger guard and pump safety
- more notable features of the fire arm include: dual extractors and i BELEIVE aluminum guts, which some say is a down side of the M590A1, although others say it works just fine.
-------------------------------------------
Remtington 870 express tactical

http://www.remington.com/products/fi...-tactical.aspx

-KEY FEATURES:

18 1/2" tactical barrel with XS® front blade sight RC Tactical (ext/ported tube)
XS Ghost Ring sight Rail (mounts to receiver)
Sight is fully adjustable for windage and elevation
Front blade sight works in conjunction with Ghost Ring to quickly and accurately acquire target
Tactical style fore-end
2-shot magazine extension
Receiver drilled and tapped for scope mounts (XS Picatinney rail with ghost ring included) its my understanding that they recently, or have not always done this with EVERY factory 870 tac, where mossburg has with all 590
also pump safety is at front of trigger guard, bit out of the way.
safety on trigger guard.


please feel free to add anything else. comments, experience, ANYTHING that is beneficial. thanks