sodapopsixtysix posted very nice Remington 870 Marine Magnum with Upgrades on Remington 870 Forum.
Nice and simple home defense Remington 870 12 Gauge 3″ Magnum setup.
TexasArmor84 posted awesome photos of the Remington 870 Police Marine Magnum on Remington 870 Forum.
You are probably familiar with how Remington 870 shotguns are made with different gauges. The most common gauge in the model 870 is the 12-gauge. This measures the diameter of the barrel. But what you may not realize is the length of the shells is also as critical to consider as their diameter. If you have 3 inches or 2 ¾ inches shells then you need a magnum receiver that can handle it. Of course, the barrel also has to be equipped to handle up to 3-inch long shells. If it is then you can fire them as long as you have a magnum receiver.
The Remington 870 Express Magnum shotgun one of their more popular pump-action shotguns and is used primarily for hunting, self defense and sport shooting. In addition, it is a very common weapon used by the military and law enforcement organizations.
Pictures from Remington 870 Forum: