A little more detail:
First, understand that the barrel needs to be round after the lug is removed, not off-center on the bottom where the lug is removed. If you cut too deep toward the bore, the finished barrel will look off center.
I determined what the closest I could come toward the bore, and scribed a LIGHT line on both sides of the lug. You just "eyeball" this.
With the barrel horizontal, I cut slots through the lug toward the bore, close but not crossing the lines I scribed. (Give yourself a "buffer" here, since you can file more metal off, but you sure can't put it back).
This allows short sections of the lug to be sawed off, and still insure the cut doesn't get too close to the bore. If the cut does start to drift, it can be corrected on the next section.
Be sure to keep the cut square to the barrel on both sides of the lug. It's very easy to start rotating the cut until on one side it's perfect, but on the other it's too close to the bore.
In other words, you're following the line nicely on one side, but the cut is drifting across the line on the other side.
To match the grained S&W finish, I buy the gray synthetic "sanding" pads at Lowe's sandpaper department.
They usually carry the same Green pads grocery stores sell as pot scrubbers, but these are too coarse. The gray pads, equivalent to 0000 steel wool do a nice job of matching the finish.
You do not need to do the whole gun, just the bottom of the lug, after using the sanding cloth wrapped around a file to remove all file marks.
This is what we use to restore the satin finish used on stainless guns anyway.
I like one of the high-tension type hacksaw frames available at better hardware stores. These have a special blade locking/tensioning device that really takes the flex out of the blade.
WATCH OUTS:
Stainless is HARD to cut. Buy a good blade suitable for stainless.
Keep well away from the final profile of the barrel when cutting. Again, you can file more metal off, but cut too deep, and you've ruined the looks of a barrel.
Buy a file card. This is a special very stiff, flat wire brush used to clean metal chips out of the file teeth. If left in, these scratch and gouge the metal, necessitating lots more polishing with the sand cloth to remove.
GO SLOW. There's no hurry. If things look like they're drifting off, STOP, and correct the cut.
Spend a lot more time polishing with the various grits of sand cloth than you would think needed.
Hope this helps.