How are mag barrels measured?

[Koosh]

Just a question, is the total length figured from the very back of the barrel (before the breach drop) to the tip, or from some other distance?

I only ask because I recently bought a 12" freak tip from a guy, and measuring the barrel from the very back makes the total length 14", while measuring from the front O-ring on the barrel makes it the 12" he said it was...

[Spray Painter]

i've always wondered that to

[ratmonkey]

i have a dye stainless in 14" for my pro-lite and in twist lock for my mag. comparing the two it seems to be measure from right after the breech at the ball detent is about right. including threading on the pro lite on they're both the same length.