Well, according to the above you need a PhD from MIT and a shop full of specialized tools to swap a S&W barrel. I guess it's a good thing I didn't know that before swapping the barrel on the Victory Model I picked up last year.
Used a six-inch vise bolted to the bench in the garage. I think it did come from Sears, actually. Special blocks? Might be nice but I used two 1X4X6 pine blocks. Used a small nail to drift the barrel pin out. No problem at all. A couple of taps and out she came.
Clamped the barrel (the original 4" had a huge bulge in it so it had to go) between the two blocks in the vise. Very tightly, I might add. Put hammer handle through cylinder window of frame. Some folks have cautioned that this absolutely will bend or twist the frame. Again, I guess nobody told this gun it was supposed to bend because with a bit of pressure the frame unscrewed from the damaged barrel as easy as pie. I did spray some penetrating oil in there and let it set over night, and of course, if you really force it when it doesn't want to come damage is certainly possible. But under normal circumstances I think this method works fine.
Had 5" M&P barrel I picked up for $5 on ebay. Screwed it in by hand after cleaning all threads on barrel and in frame. Hand-tightened about 10-15 degress shor of top dead center. Clamped in vice and tugged it into place. Took a couple of tries to get it right where it needed to be, but got it there. Held up to light and looked like barrel pin hole was aligned with notch in barrel. Put feeler gauge on barrel/cylinder gap and it was .007. Maybe not quite as tight as a perfectionist would want, but it was within specs.
Worst part was getting pin back in. Had terrible time. Later learned that pins are mated to barrels. Had to polish pin on wire wheel (also from Sears, BTW) and it did eventually go in.
Despite the warning above regarding the ejector rod, mine worked fine with no adjustments needed. At the range the pistol fired and ejected empties with great monotonous regularity.
Now, understand that I was working on an old gun that I bought for $60 because it was damaged. I figured I had little to lose in trying this myself. It just wasn't worth paying a gunsmith $100 to do this. Also, I was lucky in that the replacement barrel pretty much fit right in. It might not have been so easy had the sight been past TDC when snugged. That would mean relieveing the shoulder of the barrel to bring it around. With a lathe, not so bad. With a file, a real bitch of a job. Same thing with the gap. Mine was close enough. Another attempt might not be so lucky. I think that if the barrel is used, and has been installed on a frame, the manufacturing tolerances are so close that there is a very good chance the barrel will almost drop in as mine did. With a new part, installation with final fitting becomes a requirement.
Like I said, I was working on what was basically a junk gun. On a nice gun, I would be careful about attempting this. But I think it can be done. Well, Hell, I know it can be done because I did it.