Remington 870 18 inch Magazine Tube Extension
Usually, magazine extension is one of the first upgrades shotgun owners get. It is understandable because standard 4+1 round capacity is very limited.
One of the popular questions: What magazine extension for Remington 870 should I get to have it flush with the barrel?
If you want to get a magazine extension for Remington 870 with 18 inch barrel, get a +2 round mag extension tube. If you want to add magazine extension that will not exceed the barrel length of 20 inch barrel Remington 870 get +3 round mag extension.