The only thing it does better than the 357 Sig is it allows a higher capacity if you feel you need that.
The 356 TSW was designed with competition in mind and higher capacity was a big plus in that game.
Only thing?! Naw. Looks like it is also quite a bit cheaper when comparing to the other calibers high powered offerings (data at the bottom). Plus it has a bit more horsepower (also, data at the bottom)......so along with the higher capacity that's actually three things it does better. Consider as well loading it is not all that fun either, apparently. A twelve-year old could load 356 TSW what with it being externally just sort of a slightly longer 9x19, but some industry types at SHOT show said that 357 SIG is not too cooperative at times when it is being put together. So that's four things it does better? Losing count here....
The first major company that starts chambering their pistols in this instead of 357 SIG...well, the SIG round will probably lose some (or all) of it's current .02% market share. Then again with power and capacity like it is showing, 356 TSW could eat into some other cartridges market share too, plus just swapping in a 9x19 barrel and spring to plink with 10 cent nine milli reloads whenever is kind of cool.
I got the inside scoop on the CorBon test averages. One string of forty-five rounds was 1627 fps out of stock S&W 5" pistol and another string was 1485 fps from the S&W Performance Center snubbie "Pocket Rocket" which is crazy as being Power-Ported it only actually has about 1 3/4" of rifling. That is 563 fpe of muzzle energy from a snub nosed J-frame. Unreal. And then think about 676 fpe from the 5 inch barrel combined With 9x19 magazine capacity. Jeez. All things considered, 357 SIG shows up as...less than. You can still get a 40 S&W barrel though and swap it out but then even the hottest 40 doesn't seem to offer more fpe.....just .044 or .045 bigger hole, but again with less magazine capacity and higher ammo cost for the hotter loads. Numbers below show which one is boss in a small or medium frame high capacity auto....and then their is the J-frame. 563 fpe from less than 2 inches of rifling? Good grief.
Buffalo Bore 357 SIG 125 grain, $30.18 for twenty rounds
1433fps 570 ft/lbs from a 4.0"bbl.
Double Tap 40 S&W 135 grain, $21.95 for twenty rounds
1310fps 515 ft/lbs from a 3.5"bbl.
1375fps 567 ft/lbs from a 4.0"bbl.
1420fps 605 ft/lbs from a 4.5"bbl.
CorBon 356 TSW 115 grain, $20.55 for twenty rounds
1485fps 563 ft/lbs from a 1.75"bbl.
1505fps 578 ft/lbs from a 3.5"bbl.
1555fps 617 ft/lbs from a 4.25"bbl.
1627fps 676 ft/lbs from a 5.0"bbl.