My 6" 66 is much later - a 66-6 made 1/03. It has a regular partial lug... and the IL! It was $349.99 new/closeout from CDNN 9/03 - a bargain (I just got their latest flyer - no S&W revolvers... sigh!). The HKS #10 speedloader works fine - as it did with my old 3" 65 from '88, which I stupidly sold. They are not unsafe with light Magnum loads, but a longer fc life will be insured with heavier loads. Shoot it and don't worry - if you wear out or crack that fc, S&W has more barrels!
Now... as to ammo. I have a couple of .38s... but I have more labelled as .357 Magnums. They have capacities, barrel lengths, and other features simply unavailable in .38 chamberings. Sure, I reload .357 Magnum cases - and keep thousands loaded on hand - as target plinkers. They top out at +P .38 Special. My home defender and pocket protector loads alike are the venerable 'FBI load' - the Remington R38S12 158gr LHPSWC +P .38 Specials - all I need. Feel free to stoke your .357 Magnums with hot loads - but I won't. Mine likely were tested with 'real' Magnums - the last time they saw them, too. My son will inherit some revolvers in fine condition one day. YMMV. LSMFT.
The L-frames were brought out to instill a greater feeling of the longevity to the .357 Magnum S&Ws. The front strap is .040" thicker, allowing a .025" larger OD fc. The gripframe is the same size - K&L frames take the same grip. The cylinder opening is taller - permitting a larger OD cylinder - and a seventh round (686+). It also would fit a 5-shot .44 Special cylinder (296, 396, & 696). Of course, with a .429" bore, even more of that fc was gone - a real 'knife-edge' resulted. Of course, the .44 Special, at least non-Keith level loads, is a lower pressure round - the fc should last (My 296 & 696 are fine.). I think the K-frames are fine... the partial/no-lug makes them unreal pointers - really an 'extension of your hand'. Buy it!
Stainz