Doggonit, I can't speak for "Old Paladin" either, but I'll answer what I can (which won't be much.
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I have one of the Benelli M1014 shotguns, serial number 7XX, but haven't gotten around to firing it yet. Believe it or not, some of my firearms have sat new in my safe for over a year before I finally get around to firing them.
The shotgun has a fixed-choke. The factory ghost rings have white dots, non-tritium. The barrel is chrome-lined. I have no experience with the Mepro 21, but I can tell you that it will be my first choice when buying optics for it. The mag capacity is 4 from the factory, but can be legally converted to 5 with the simple removal of an internal 1-shot red plug. And if you switch to the synthetic field stock, you can legally add the 2-shot mag extension, giving you 7+1+1. The "hump" on the bottom of the receiver is not on the military or civilian versions. I believe it was just on the early models. I cannot even recall what its purpose was. As for the finish colors, mine is black, the color it is designed to have. The purple ones are definitely a flaw (as stated by Benelli), and I have only heard of one. The four that my dealer HAD were all black ones.
The accessories available for the M4 are as follows:
81040 Pistol Grip Stock
81041 Standard Synthetic Field Stock
81042 Fixed Telescoping Stock W/ Pistol Grip
81043P Two-Round Magazine Extension
60795P Ghost Ring Tritium Inserts
Call Benelli USA at 1-800-264-4962 and request a free two-sided color M1014 brochure. I did and had mine laminated.