the length is typically measured from the tip of the barrel to the end of the breach of the gun, so the most likely reason for this is one barrel screws in more or less than another barrel, but the length on the gun should be the same for all barrels said to be the same length
QuencyJones16 "Listen to me and Rygor, we know our junk...."
PunkAnarchist69 "I highly respect your opinion Rygor you know your stuff"
EvilOgre8705 "Damn Rygor....I mean good job...you seem to know ur ****..you couldn't have said that better"
Guns only lead to problems…But when they come we will be ready to blow their freaken heads off