Does anybody know...

[Samster1123]

I'm still confused about it having no markings.

 

[mapsjanhere]

Have you taken it out of the stock? If it's European it will have proof marks underneath the barrel. So I'm still thinking it's related to the Ward brand shotgun I linked, that knurled nut underneath and the square magazine are pretty unique. Since Montgomery Ward didn't make their own guns it's probably a rebranded Mossberg or Stevens.
Found a picture on a Gunbroker auction for a Ward Westernfield that looks very close to your action

 

[Samster1123]

Okay. But is the mag detachable?

 

[mega twin]

looks like a mossberg 20ga. to me.

 

[ZeSpectre]

No bolt, no trigger group, etc.....it's not a gun, it's a simulation

 

[fal308]

Are there any levers, buttons, recesses etc in front of or behind the magazine?
Take a picture of the magazine area from the underside, including just in front of and behind the magazine. Then someone should be able to tell you if its detachable.