Ummmm...wait. S&W had a habit of altering the heat-treat for varying power levels. I don't know if that's a factor here, but I'd damned well find out before doing this.
You can definitely take your 28 up to a 44Spl with no problem...but research is needed before going to a 44Maggie.
Now. There's another very interesting option you might consider, esp. if you're a reloader. Actually a pair of similar options. You have your cylinder removed and sent off to be reamed in one of two wildcats: 356GNR or 38/44 Bain and Davis.
The 356GNR is something Gary Reeder came up with: a 41Mag shell necked down to 357, firing 357-type bullets. By increasing the case volume pressure drops for the amount of work done. Some of his loads exceed many factory 44Mag energy levels
although that's easier to do with a single action platform. Still, a 180gr at 1,350fps is nothing to sneeze at, neither is a 125 at 1,850(!).
http://www.cartridgeperformance.com/our_cartridges.htm
Cartridge Performance sells brass, loaded ammo...Gary Reeder reams the cylinder (you just ship him that) and can sell you reloading dies. No changes to the barrel, frame or the rest of the gun are needed. Use factory speedloaders meant for N-frame 41Magnum guns.
The 38/44 is even more psycho, based on a necked-down 44Mag shell. Hornady sells the dies, the Bain and Davis gun shop in California is still in business and can ream the cylinder, probably sells everything else. NOTE: there have been two versions of this concept, with a different shoulder shape on the "Mark 2". You want the later version, and that means your reloading dies and newly reamed chamber have to match. OK? The new version eliminated the "shell setback" issues of the early variant. There are some sources calling the Mk.2 "357/44B&D" including the son of the original inventor on one web-forum, so that may be the terminology used at the B&D shop.
You won't be able to seriously exceed the 356GNR power levels but you'll pass it by a bit. Get too crazy with either and your first warning is when the shells will try and squirt out the back on firing, putting enough pressure on the recoil shield and slowing down cylinder spin. Basically, if each shot is making the trigger pull a lot worse, whoops, too much. But it takes quite a bit to do this and meanwhile you've passed 357Mag power levels WAY in the dust and it's pretty easy to top most 41Maggie loads too in terms of raw energy.
For max fun, start by having a second 357Mag cylinder fitted to your gun, and then ship one off for reaming. You'll then have a "double caliber gun".
