Here's my minimal tools shotgun barrel cut-down procedure:
Measure the existing barrel by closing the action (make sure it's empty) and putting a dowel rod or cleaning rod down the barrel.
Mark the rod even with the muzzle, remove it and measure from the end of the rod to the mark.
This is the actual barrel length.
Measure the rod to the length you want the barrel to be and mark it.
The barrel MUST be at least 18" long, and if you're smart, you won't go under 18 1/2".
After marking the rod at 18 1/2" or how ever long you want it, lay it along side the barrel with the FIRST mark even with the muzzle, then mark the barrel at the second mark.
This will be where the barrel will be cut.
STOP...... Start all over and measure everything AGAIN to be SURE.
Make sure the action is closed when you put the rod down the bore, and make SURE you measure everything RIGHT so the cut line isn't less than 18 1/2".
A smart man measures everything several times. Cut too short and you just committed a FELONY.
Once you're sure about where you want to cut, carefully wrap a piece of tape around the barrel, keeping it as square with the barrel as possible.
Buy a good fine-tooth hacksaw blade and use it in a good high-tension saw frame.
When you're ready to make the cut...STOP... check everything out again one last time.
When you're sure, make a one or two stroke gentle cut on the tape cut line. Then rotate the barrel and make another one or two stroke light cut.
Continue this until you have a shallow line cut all the way around the barrel.
Continue making one or two stoke cuts and rotating the barrel until the barrel is cut through.
Doing it this way insures you make a square cut that doesn't drift off and make the muzzle uneven.
This prevents having to do a lot of filing to try to square the muzzle up again.
Once the barrel is cut, use a fine-cut file to carefully remove the saw marks from the end of the muzzle, then use the file to break the sharp outer edge.
Wrap fine metal-type wet or dry sand cloth around the ball of your thumb, and use that to break the sharp inner edge of the muzzle.
Use cold blue to touch up the cut edge.
For a new front sight, either have a gunsmith install a new bead, or buy a Remington type bead and base unit from Brownell's, and soft solder it on by "sweating" it in place.
Brownell's sell this as a "Colonial Arms" front sight base, item number 198-104-101.
To solder the base on, use a fine-cut file to remove a spot of bluing from the barrel that is JUST as large as the new base. (solder won't stick to bluing).
Clean the base of any grease, heat it up, flux it and apply a thin coat of soft solder. I recommend the 3% silver content soft solder sold by most hardware and Walmart's. This melts at under 450 degrees and makes a good bond.
Apply a thin coat of flux on the bottom of the base, then clamp it on the barrel.
Heat the barrel until the solder melts then allow to cool.
Clean everything up and you're in business.
Another option is to use the new "Black Max" bonder made by Loctite and sold by Brownell's.
This is a "super-glue" mixed with a black rubbery binder that's specifically made to bond on shotgun sights. From all reports it really holds if you do the job right.