How to measure shotgun barrels ?

[TrustMyG23]

Hello there!

I've searched for the ways to measure a shotgun barrel and i'm still not so sure. A picture describes a thousand words, so please post pictures of how to measuring a shotgun barrel or a video. Thank you!

[demusn79]

Don't have a pic but you put a tape measure down til it stops and read to the end of the barrel.I leave an extra 1/2" to be safe when cutting at minimum.
18 1/2"

[TrustMyG23]

With the place that feeds the bullets closed ? thank you

[CAcop]

The action must be closed as if it was going to fire. The chamber must be empty. It is from the breechface to the end of the barrel. IIRC the ATF uses a metal rod that is marked.