What size is my barrel?

[Bill_1202]

I have an 870 tactical express magnum. How can I tell what size my barrel is? 18" or 18.5"? What points do I measure? I want to get the Remington +2 Mag Extension but that don't want it to protrude beyond my barrel. I'm told it won't if my barrel is an 18" barrel?

[BigMike67]

from what i understand you put a small tape measure inside the barrel and run it down to where you hit the bolt.... i measured from the front of the ejetion port and came within a quarter of an inch ..

[Synchronizor]

The legal definition of shotgun barrel length is the distance from the closed breechface to the muzzle (or the forward end of any permanently-attached muzzle device). Shooters and gun manufacturers define it pretty much the same way, though sometimes fixed muzzle devices are ignored, or removable ones (like extended choke tubes) are included. For plain barrels though, it's pretty straightforward. Close the action (unloaded, of course), insert a dowel or rod, mark, remove, and measure. A sufficiently-thin tape measure or ruler works, too. You can also measure the barrel by taking it off the gun, and running a tape measure from the back of the chamber to the muzzle: