The Mossberg looks more like this shotgun to me http://www.gunreports.com/news/long_guns/Mossberg-590A1-Tactical-Shotguns_1030-1.html
So youve found the word "Rhett" in a lot of places, but do you have any actual leads, or are you just dumping everything you find?
Also, could you please say WHY you think it resembles the Mossburg 590-A1?
All of the guns that have been identified have very exact similarities. For example, lets look at the CARB-9, one of the few guns that isn't as obvious as many of them are. The body and front end are from the SU-16E. Everything from the pins holding the upper and lower together, the line where the two meet, the horizontal line in the middle of the upper, magazine release, raised thumb rest on the grip, slightly curved trigger guard, safety behind the trigger, and slightly-curved oversized magwell that makes no sense with a 9mm mag, not to mention the half circle cutout on the magwell and the vertical line above it. The stock is from another variant of the weapon, the SU-16B.
The Mossington on the other hand, is much harder to pick out details for, since shotguns are so similar to one another. The only feature I can actually identify is the stock which is clearly from the XM1014. The rest of the features are rather generic when it comes to shotguns, or so highly stylized that they no longer resemble anything real.
Something that might be a clue that I haven't been able to find a real world gun with is the body. The body of the Mossington appears to have a large hinge at the bottom and a seam down the middle, implying that it could be opened like a top-break revolver (Ex. Caesar/REX). No shotgun i know of or have seen does this. Most shotguns are advertised by the fact that they have a one-piece or even a milled body.
If I could see the internals of the gun somehow, I could pinpoint the weapon it was based on, but I highly doubt its even a part of the game, no reason for it.
You are right in a sense though, this is one of the few weapons I'm still not 100% convinced on, but I have yet to see anything closer than the 1014.
The mossington (mixture of Mossberg and Remington are the leading shotgun makers) the weapon is a semi auto 12g that is influenced by the Benelli M4 the Mossberg 590A1 is a pump action shotgun.
The "speaker" thing is possible, but I'll wait to see what people have to say in a few months. Most of the difficult names really clicked when we finally found the reason for them.
As for the Mossington, even though the 1014 is semi-auto, the in game weapon is pump-action. The gun is pumped every time its fired in game clips, and the charging handle that would be required for a semi-auto is missing from the skin. Some people have claimed that this proves the Mossington is not the 1014, but it could be no different than SD basing the Drognav on the DSR-1 (bolt-action) yet making it semi-auto.