Skunky, you're missing a couple of things.
First, even in "rifle calibers" you're discounting the ammo capacity of the levergun. The most common Marlins in 45-70 have five shot tubes (plus one up the pipe it's a sixgun) but special runs of longer barrels with up to nine rounds factory capacity is available.
45-70 ballistics stomps hell out of the shotty slugs.
Second, you dismiss "pistol calibers" too quickly. In the case of 45ACP, 40S&W and 9mm that may be warranted, but NOT in 357Mag or 44Mag.
Example: here's some velocity data for some really hot 357s in an 18" barrel carbine (plus some others):
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Make special note of the Marlin 1894, 18.5 inch barrel velocities. Item 19C/20, supercedes 30-30 energies!!!
1. 3 inch S&W J frame
a. Item 19A/20-180gr. Hard cast LFN = 1302 fps
b. Item 19B/20-170gr. JHC (jacketed hollow cavity) = 1299 fps
c. Item 19C/20-158gr. Gold Dot = 1398 fps
d. Item 19D/20-125gr. Gold Dot = 1476 fps
2. 4 inch S&W L frame Mt. Gun
a. Item 19A/20-180gr. Hard cast LFN = 1375 fps
b. Item 19B/20-170gr JHC = 1411 fps
c. Item 19C/20-158gr. Gold Dot = 1485 fps
d. Item 19D/20-125gr. Gold Dot = 1603 fps
3. 5 inch S&W model 27
a. Item 19A/20-180gr. Hard Cast =1398 fps
b. Item 19B/20-170gr. JHC = 1380 fps
c. Item 19C/20-158gr. Gold Dot = 1457 fps
d. Item 19D/20-125gr. Gold Dot = 1543 fps
4. 6 inch Ruger GP 100
a. Item 19D/20-125gr. Gold Dot = 1707 fps
5. 18.5 inch Marlin 1894
a. Item 19A/20-180gr. Hard Cast = 1851 fps
b. Item 19B/20-170gr. JHC = 1860 fps
c. Item 19C/20-158gr. Gold Dot = 2153 fps---- Can you believe this?!!!
d. Item 19D/20-125gr. Gold Dot = 2298 fps---- Or this?!!!
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See also:
http://www.buffalobore.com/ammunition/default.htm#357
Jim again. That's a 10rd capacity gun, son
. And it's VERY compact and handy. Out to 200 yards, those loads are as effective as anything available for combat...slap a scout scope on it, and you are NOT undergunned if you're familiar with 'em.
Reload speed is no worse than a shotty.