Shots are a rather unique firearm in that they can have absolutely devastating terminal ballistics. However, they do have a severe limitation in that they have a low capacity and take a significant period of time to load. This is one of the reasons why many people choose to mount extra ammunition to their shotgun. There are many ways to go about this, but the Mesa Tactical Aluminum SureShell carrier is among the best options.
This shotgun sidesaddle mounts using your trigger group pin hole. This is a solid mounting point that puts the side-saddle on the flat side of your shotgun receiver. By placing your ammunition in this location, it is very close to the ejection port, as well as the loading port. So, whether you need to port load or load the magazine tube, the shells are held very close to where they need to go.
This shell holder is made to be tough and put up with hard use. As oppose to some other nylon or plastic shell carriers, this piece is machined from 6061-T6 aluminum. This gives this shell carrier excellent strength and durability while only adding minimal weight. The shell carrier is bead blasted and finished with a mil-spec hard coat anodizing for a corrosion and wear resistant finish with minimal glare.
To ensure that the shot shells stay in the carrier and off the ground, a santoprene elastomer is used to interfere with the shell bores to retain the shells.
When installing this device on a Mossberg 500/590, it will only fit on the left side of the receiver. Additionally, only limited forends may be used. You must use a tactical forend that does not significantly overlap the receiver. Alternatively, you could use a factory forend that has been modified.