The K-frame 19 and 66's were designed to shoot a 158 gr , or heavier bullet . S&W had received so much flak that the 27-28's cylinder was too short to load the " Keith " 173gr " swc in a 357 case . So , with the development of the new , at the time K-frame 357's , they lengthened the cylinder to accept the Keith swc in a 357 case . You don't have to go to a heavier bullet , just use the 158 gr as the lightest . I personally woudn't worry about jacketed bullets causing undue wear on the barrel . The velocity is too slow , not like a high powdered rifle blazing along at over twice the velocity .
The L-frame has the same longer cylinder .