So I finally got this project all done between March and now, and thought I'd post some pictures for all to enjoy.
The project started off as a Mossberg 500 "tri-rail", which is a standard 500 that comes with a railed FAB defense forend and an ATI pistol grip / AR stock adapter and a 5-shot shell carrier attached to the stock.
The first thing I did was install a sling swivel stud on the takedown screw. I used the swivel stud off my SR 22 that had been sitting in the parts drawer since I put a quad rail on it. It required cutting down but after taking a large chunk off with a grinder, fine touches with a file and using a die to clean up the lead portion of the threads, it indexed correctly when the takedown screw was tightened.
Next I installed a Mesa tactical receiver rail, and threw on the lowest mounting red dot I had, a Bushnell zoom dot. I mounted it using Leupold vertically split rings.
The reason I went with the vertically split rings was to provide shell clearance for the Mesa tactical 6 shot shell carrier. The carrier mounts to the shotgun by pivoting on a special nut & bolt you replace the ejector bolt with. It is then fixed into position using a chicago screw which replaces the trigger group pin.
I replaced the follower with a no-jam follower. I had a bad day turkey hunting once with my 535 when the follower and spring decided to make sweet love in the middle of the morning.... so since this gun was built to lean up against my bedside more than anything, reliability is key.
Next I replaced the ATI grip/adapter (for sale!

) with the NEA adapter. The ATI adapter despite being all polymer was surprisingly robust, but ultimately I hated the grip. I got the NEA adapter and got a commercial buffer tube & castle nut, while retaining the ATI buttstock that originally came with the shotgun. It's the same stock as the "strikeforce", but it did not come with a cheek riser. Fortunately I had one laying around and installed it at its maximum height, giving me an excellent cheek weld with my red dot.
The NEA adapter is really nice and you just can't beat the feeling of metal. It came with an A2 grip which I replaced with a hogue. I should note that the bolt supplied with the adapter that screws into the receiver was long enough, but not as long as it could have been. I took a longer bolt, and after carefully observing how much it jut into the receiver, cut it down for maximum thread engagement.
All in all, the gun feels very solid and now that its finally all together I can take it out and see how it shoots!
It would have been cheaper to buy a regular 500 than the "tri-rail" version, but what can you do.
Parts list:
Frontier Firearms:
Mossberg 500 12ga "tri-rail" 5+1 - $420
S+J Hardware:
Mesa Tactical receiver rail - $35
Mesa Tactical shell carrier - $70
No-Jam follower - $12
FAB Sports:
Commercial buffer tube - $37
castle nut - $12
AR stock wrench - $12
SFRC:
NEA Mossberg AR stock/grip Adapter - $90
Dlask Arms:
Hogue AR grip - $17
EE:
Bushnell Zoom Dot - $200
The Gun Centre:
Leupold low 30mm vertically split rings - $25
Parts Bin:
Cheek rest for ATI stocks
Sling swivel stud
Burris low 30mm ring
LED light
Grip panel
Sold:
Stock-mounted shell carrier - (-$30)
Total project cost: Approx. $900 before taxes & shipping.