MODEL M1B:
Small size guns such as:

Autos— .22, .25 and .32 caliber handguns: Beretta's Bobcat & Tomcat, Kel-Tec P-32 & P-3AT, NAA Guardian's, Raven Arms, Seecamp's, Taurus PT-22, PT-25 and many other similar sized guns.

MODEL M2B:
Medium to large guns such as:

Autos— AMT Backup .45-- Astra A-75 -- Beretta 9000's, Cheetah & Px4 Storm -- Browning Pro & Hi Power -- Colt 1911 All Models -- GLOCK 17,19, 26, 27 -- H&K Compacts -- Kahr -- Kimber -- Para Ordance -- S&W Sigma series, SW99, M&P, 410, 457, 908, 910, 3913, CS Series -- Sig Sauer P228, P230, P239 -- Springfield Armory 1911's & XD's -- Taurus Model 92, 100, 24/7 & Millennium series -- Walther PPK/s and many other similar sized guns.
Revolvers—Small J-Frame 5 shot, 2-3" barrel revolvers: Charter Arms Off-Duty, Undercover, Bulldog, Mag Pug & Pathfinder -- S&W J-Frame All Models -- Colt Detective Special -- Rossi -- Ruger SP101 -- Taurus Model 17, 605, 650, 85, 850, 851 -- and many other similar sized guns.