TacStar's Slimline SideSaddle helps to improve reload capabilities and efficiencies for shotgun receivers. It utilizes a non-glare, anodized aluminum backing plate with a contour to the plate so that it takes up less space on the receiver, while the shell carrier itself is made of flexible synthetic rubber material. This model is compatible with your 12 gauge Mossberg 930.
Specifications:

Type	Shell Holder
Color	Black
Material	Aluminum/Rubber
Size
Model	Mossberg
Finish
Model Fit	Mossberg 930
Mount Type	Buttstock
Belt Size
Shell Count	6
Caliber or Gauge	12 Gauge
Compartments	6