1. .22 LR-only because it includes rifles and handguns.
2. .30-06
3. .45 ACP
I hate posting anything online that says to the world that I have a firearm, let along multiple firearms. But what the hey, in for a penny in for a pound.
I think .38/.357 is #1 by a slim margin. All handguns
.22 LR in 2nd. More rifles than pistols
.45 ACP solidly in 3rd. All handguns
.44 Mag/ Spl. 4th. All handguns, but one.
I think .30'06 and .223 are tied for 5th.
Since one of my collecting 'niches' is US Military rifles , and with most makes and variations of the 1903/A1/A3 , 1917 , and M-1 Garand , the 30-06 wins with almost 2 dozen. Plus a lesser number of like chambered commercial sporting rifles.
It's been a while since I've taken a group S&W photo, so this photo doesn't show them all but this is how the current inventory count came out.
.38 Spl x 53
.357 Mag x 49
.44 Mag x 19
.22 LR x 16
.32 H&R x 12
.45 APC x 11
.41 Mag x 9
.44 Spl x 9
.45 Colt x 9
.22 WMR x 7
.32 S&W x 4
.38 S&W x 4
10 mm x 4
.22 Rem Jet x 3
9 mm x 3
.17 HMR x 1
.356 TSW x 1
.40 S&W x 1
.44-40 x 1
.455 Mk II x 1
.500 S&W x 1