I made a tool the other day for removing a Mosin barrel, this was the motivation for that.
I cut 4" off the barrel and shortened the front of the stock about the same amount. I also turned down the end of the barrel and reinstalled the original front sight.
I fired it off the back porch a few times on new years eve, my son said it was about a four foot fireball, my wife said it lit up the whole back yard. I'll have to see if I can get the wife to try to get a picture of it.
The original cabine barrel is 20.4", I cut 4" off and after I cut a new crown on it the barrel came out to about 16 1/4".
Haven't fired it in the daylight yet....The barrel on this one wasn't great to begin with which is why I decided to cut it up, so i'm not expecting pinpoint accuracy, but i'll try it out sometime in the next couple days and let you know.
Once I got the tool made the barrel came apart easier than I expected it to. If you don't intend to reuse (or even save) the old barrel it could probably be done without the clamp/wrench. You would need a lathe though.