I have several CO2 BB pistols.
I still have my first which is a Crosman 38C . Its missing the barrel liner and the valve body has been rebuilt several times, but finally the threads stripped. If I ever find one I can strip for parts i may try to rebuild it again. Its very stoutly built with thick machined brass valve body, not at all like the latter models.
My favorite now is a Crossman /Urmarex/ Walther PPKS. Its a metal blowback with smoothbore barrel. Not very powerful, but kicks more than a .22 pocket pistol, so it gives the illusion of shooting a real PPK.
I have a Gamo replica of a SIG .380, DOA .177 BB repeater with rifled bore for single loading pellets. The DA trigger pull is much like that of my I frame Handejector.
I also have a replica of the S&W 59, representing a later model than my Model 59 but with similar styling.
Its not heavy enough to provide realistic practice, but learning to control a heavy DA pull with such a light pistol does seem to help in controling the real thing.
Both the BB gun and the real Model 59 have rather sloppy DA pull anyway.
My best CO2 pistol is the S&W 78g in .22 caliber. A very accurate single shot with fully adjustable target sights. Sturdy cast alloy construction, a beefy BB pistol with excellent trigger pull.