Shotgun selection advice

[sumpnz]

I want a shotgun to hunt ducks and elk.  Bear with me.   I know very little about scatterguns.  I have a couple 20ga shotguns but they’re not suitable for several reasons. 

I hunt elk by kayak in the tidal zone of rivers on the Olympic peninsula.  I jump tons of ducks paddling around looking for elk.  Enough at close enough range that I could probably average close to a limit most days. Some days, primarily when it’s warm (50’s) and sunny, it’s almost pointless to hunt elk as they hunker down until it’s 40’s and raining sideways, and being able to switch to ducks would be really nice.  Or at least hunt ducks in the morning and then switch to elk for the afternoon. 

For ducks you need instant access to the gun, which means it’s going to splashed with brackish water quite a bit.  With elk you generally have way more than enough time to extract the rifle from a dry bag, so it’s tolerable to use a blued/wood rifle.  So for ducks stainless steel is a must, and synthetic furniture would be highly desirable vs wood.  There are some wildlife refuges where centerfire rifles aren’t allowed, but shotguns with slugs (and muzzleloaders for that matter) are allowed.  So any shotgun should enable us to expand to hunting those areas too.  12ga is the minimum to be legal for elk with a shotgun.

So, what I think I’m looking for is a stainless/synthetic, 12ga shotgun that is reasonably available with both bird length barrels (swapable chokes highly desirable) and slug barrels.  Cheap is good, both to keep it initially affordable but also because even with stainless and synthetic setups and daily cleaning/oiling that environment will be harsh and I’d rather replace corroded parts or the entire gun for something inexpensive than with something really high end.

I’m not very picky on action type, but pump or semi-auto would probably be preferable to double barrel (whether SxS or O/U).  I suppose bolt action is fine.  I suspect lever action (if such a beast exists) would be too finicky to survive very long in that environment.

What says the hive mind for my best bet?

[charby]

I used to waterfowl and I used a Benelli Super Black Eagle, blued and synthetic stock. I still use it as my primary upland and turkey shotgun. It got dunked a few times hunting waterfowl and nothing a little spray can gun oil couldn't fix when I got home. I was a over decoy/call hunter. Never had that good of luck trying to jump ducks from a canoe. They are fast.

Before Iowa allowed specific rifles for deer hunting, I used a  Remington 870 with a Hastings cantilever fully rifled 24" barrel. With hand loaded slugs I could hit a playing card at 150 yards and I did drop a deer at over 200 yards with it once.

You are going to have a hard time finding a stainless shotgun.

[Ben]

When I moved here, I bought a Benelli Super Nova pump gun for waterfowl. It has a tough, weather resistant camo finish and handles and shoots great.

That said, Benellis aren't the cheapest shotguns around, and if it were me looking for what you describe, I'd just look for a deal on one of the weatherized finish 870s or Mossy 500s. Lots of barrel combos out there, and I know that some of the receivers come with picatinny if you want to mount an optic for the elk, then just pop it off when you switch to the bird barrel.

[HankB]

There are more "weather resistant" coated shotguns around than there are stainless shotguns. I came across an article that discusses some of the various coatings here: https://www.outdoorlife.com/story/guns/evolution-of-best-shotgun-coatings-from-blued-barrels-to-cerakote-and-other-finishes/

Using the same gun for waterfowl and big game at 100+ yards with slugs? I'm sure there's something that will do the trick, and it will be either a pump or semi-auto, not a SxS or O/U. I don't know if you'll find something cheap that will still work well.

Aside from the exterior, spraying the internals with something like Corrosion-X (NOT WD40!) might be a good idea.

[Hawkmoon]

https://www.mossberg.com/590-mariner-9-shot-50299.html

[sumpnz]

https://www.mossberg.com/590-mariner-9-shot-50299.html

Great for repelling pirates.  Not so great for waterfowl.  No ability to change choke tubes, and a much shorter than typical barrel for birds.  Might be able to shoot rifled slugs ok, but with just a bead sight the accuracy would limit me to 50 yards probably.

I like the action though.  If I could get stainless bird barrels, and a slug barrel (doesn’t have to be stainless) that would fit the action it would be a good idea.

Oh yeah, I’d also to be able to plug the mag tube such that it would be legal for waterfowl.  2+1 capacity is federal regulation for waterfowl hunting.  And any plug in the mag tube has to such that it can’t be easily removed in the field.

[Tuco]

- developed thoughts and edited-
Stainless shotgun barrels aren't the same as stainless rifle barrels. As far as I can tell, the thin walls of a wingshooting scattergun aren't compatible with stainless metallurgy.  Rifle and pistol barrels are thick walled, so it's compatible (I'm not a steel guy, but thin steel needs an "elasticity" to handle pressures, and my assumptions have not been subject to rigorous fact-checking).
The purpose-built defensive shotguns such as the linked marine magnum, I personally wouldn't try to hit a duck with one.  Short barrels are hard to swing (yes you _do_ need to swing on rising ducks) and the stocks are designed for a cheek weld (with a low comb you'll need to fully cover a rising target with the barrel to hit) I've shot rounds of skeet with defense setups. They weren't very memorable.
If you're dead set on stainless in one form or another, I'd check if the marine magnums can accept a standard blued barrel and a field buttstock. 

On the other hand, if you want to hit ducks, keep the elk gun cased until you need it, nothing to be gained by swapping barrels in the field.

I suggest a field grade 3" 500/870 with a plastic high comb (hunting, not clay or defensive) stock and a 28 or 30 inch threaded barrel.  Or Ben/Charby's Benelli. The most important options in your situation are a warm water hose attachment and a case of CLP. It may rust, it may go overboard, you might need to jam seaweed in the magazine because you forgot the plug, it might get bent from using it as a push pole (unloaded of course!)
Sometimes a tool is just a tool, and we spend a lot of time chasing our tail when we could be hunting.