To dispell the myth, a S&W 642/442 and 340PD are exactly the same size - and would be indistinguishable in the dark - except for the weight. The 642/442, of Al alloy frame and SS cylinder and barrel, weighs 15.0 oz. The 340PD, of Al/Sc alloy frame, SS barrel, & Ti cylinder, weighs 11.4 oz. Both come gripped the same - with a painfully dimunitive open-back boot grip.
Shooting the Remington R38S12 +P 158gr LSWCHPs from the 642, which chrono-ed 840+ fps, is not 'fun'. There is some recoil - but the dimunitive grip is the real culprit - there is nothing to hold on to! Larger grips take it out of the pocket carry realm, however, so one learns to 'live with it'. Go to a 340PD and some hot CorBons, and real misery can be your's. A helluva hand slap, which tries to rip the small grip from your hand, is accompanied by an earsplitting 'crack' and unreal illumination - even outdoors in decent light. Indoors, you'll damage your hearing - and - if fired at typical 'intruder' distances, you'll likely cauterize any wound you inflict - and start his funeral pyre. A friend invited me to shoot his so loaded - at an outdoor range. Yeah, one shot should have been enough... but no, this idiot had to try a second. Easily the most miserable handgun I'd ever shot - and I've shot nearly everything. He had shot only regular .38s from it - with gloves - and still didn't like it. He bought it 'because .357 Magnums are great for personal protection', or so he was told at the gun store.
The 'mission' of a .357 Magnum should always be recalled. It was an improvement over the .38/44 - devised to to hole car doors and wound fleeing felons in the thirties for J. Edgar's 'G' men. The LEO handgun of the day was a .32 or .38 S&W; .38 Special, even, was a luxury. Bad guys often raided National Guard armories - and carried everything. S&W made a masterpiece in the .357 Registered Magnum - and proved it's utility as a hunting handgun round, too. Do we need it today for personal protection? I don't think so - and voted, as I said in my earlier post, by keeping +P .38s as protection, and my .357 Magnums for 'hobby' uses. So, .38 Special only revolvers have a function in my life. YMMV.
Stainz
PS Just FYI: MSRP - 642 $600; 340PD: $1,122 (from '09 S&W catalog)