It depends on the era when the revolver was made.
In the beginning, just after World War Two, S&W introduced a series of target revolvers in calibers .22, .32 Long and .38 Special. They were called K-22, K-32 and K-38 Target Masterpieces. All had barrels with narrow ribs. Later, the ribs on the .32's and .38's were made wider so that the revolvers would be equal in weight.
During the time when the K-38 had the narrow rib, various law enforcement officers (FBI Agents in particular) sent back K-38 Target Masterpieces (pre-model 14) to the factory and ask that the barrels be shortened to 4 inches and a Baughman "quick draw" front sight mounted in place of the target one. The modified gun became so popular that S&W introduced it as the K-38 Combat Masterpiece (pre-model 15). This revolver retained the narrow ribbed barrel. The K-22 Combat Masterpiece (pre-model 18) was a .22 caliber understudy used for training, and other then being a .22 revolver was identical to the .38 Special version.
So what is the difference between the K-22 Target and K-22 Combat versions?
The Target model came in barrel lengths of 6 or 8 3/8 inches, and had a patridge front sight. The Combat one came with a 4 inch barrel and a Baughman "quick draw" front sight that wouldn't snag or rip a holster.
In later years S&W dropped the K-22 Combat Masterpiece (model 18),
and added a 4 inch barrel length to the K-22 Masterpiece (model 17).
All of this should now be clear as mud...