This SBS (short barrel shotgun) started as an 870 Police Magnum, the strongest Remington 870 (and many would say the worlds best pump shotgun) with many parts added: A Vang Comp barrel, Knoxx SpecOps Stock, LPA sights, VCS Big Dome Safety, One Shot Tactical Magazine Extension with Side Sling Mount and a a rail mounted to the top of the receiver (for a red dot, etc)

The Vang Comp System
Modifications to Shotgun Barrels
(from their website)
The Vang Comp System (VCS), designed by gunsmith Hans J. Vang, is a set of modifications to shotgun barrels. The alterations to the barrel consist of lengthening the forcing cone, back-boring the barrel, and adding compensating ports. With the VCS, accuracy significantly improves, felt recoil is dramatically reduced, and muzzle rise diminishes. By lengthening the forcing cone, the pellets have a smooth flow from the chamber to the bore. This prevents the pellets from bunching up in the barrel and reduces the felt recoil. In addition, the pellets do not become as deformed and keep a more consistent shape.

One Shot Tactical Magazine Extension with Sling Mount. Also replaced the factory spring & follower with a extra-power magazine spring and a high-visibility stainless steel follower

It's really a perfect length for quick use while retaining great performance and magazine capacity (5+1)

VC-BDS Vang Comp Systems. Easy-To-Locate, Quick-To-Disengage. Large, dome-shaped button is quick to locate. Just a quick push with the side of your trigger finger will disengage the safety. Round profile does not snag clothing or guncase liner. Drop-in installation

Knoxx SpecOps Stock
(From their website)
From the longest arm of the law to the shortest, the Knoxx SpecOps Stock is instantly adjustable to fit any shooter. With over 4 inches of adjustment, this is a stock that the entire department can use comfortably in any application and with any load.

Just when you thought recoil reduction had reached maximum potential, Knoxx Industries has produced yet another patented recoil-reducing stock to revolutionize the way you think about shotguns. Utilizing dual Knoxx recoil-compensating systems, the SpecOps Stock has the ability to reduce felt recoil of even the most potent loads by up to 95%. The SpecOps Stock makes even the heaviest loads easy for all shooters to handle!

The SpecOps’ polymer and alloy construction makes it durable, reliable and built to last. Also, the unique features and design of this pistol grip style stock allows law enforcement agencies and military personnel the ability to use their shotguns with all load-bearing and ballistic tactical vests.

Designed to fit any and all shooters, and practically devoid of recoil, the SpecOps Stock is the latest in the Knoxx family of recoil-reducing products. Not only is it utilizing two recoil-absorbing mechanisms to soak up recoil, it also adjusts to fit any shooter regardless of the situation or application.

Hunters and competitive shooters will find their scores and hit ratios improving as flinching and recoil anticipation dramatically decreases.

It's also got a rail installed on top to allow for an optic like a red dot, EOtech or Aimpoint