I would absolutely stay away from the Ruger MKIII pistol. It was such a bad variation that it forced the company to come out with the MKIV. My buds who bought MKIII's, bought Volquartsen parts and converted them to the MKII configuration.
This is the best of the MKI, MKII, and MKIII, a MKII:
A Bullseye bud of mine purchased a MKIV and he loves it. I have been shooting my Ruger MKII's in bullseye competition and I recently added the Volquartsen trigger. I do not recommend the Volquartsen hammer or sear if you have a crisp trigger pull, but the trigger is adjustable for over travel and take up. I was disappointed in the sear/hammer set as the trigger pull had a lot of creep. I would not been able to install the trigger, sear and hammer, without help from Utube.
A lot of folks, including myself, still feel that Ruger should have quit with the Mark II version, but, they didn't. Instead, they introduced the Ruger Mark III version , when a "lawyer" took over the helm at Ruger. The Ruger Mark III is not a BAD pistol, and it does include versions with barrel lengths that the Mark II did not incorporate. Two alleged, safety devices, were added to the Ruger Mark III, a loaded chamber indicator & a magazine disconnect feature whereby the pistol could not be fired unless the magazine was installed. Both dumb ideas are easily thwarted for less than $50.00. A good feature: The magazine release on the Mark III is much more "fumble-free" over the now 1911 style release located at the front of the trigger guard. My personal Ruger Mark III will compete, accuracy wise with the Mark 5½ bull barrel pistols I own. the only Ruger Mark II pistols I have that are more accurate than the Mark I Target, Mark II & III Competition Targets, Mark II Government and my Mark IV Competition Target, are the two Ruger Mark II 10-inch barreled version in blued and stainless steel. Even my long sought after Ruger Mark III 4¾ Hunter shoots just as good as my bull barreled Mark II pistols:
The Ruger Mark IV is another answer to a problem that never existed. Difficulty with reassembling the upper, to the grip frame, after basic cleaning. Less than 3 months after the introduction of the Ruger Mark IV, there was a recall on every pistol sent out of the factory. The claim was that
IF, when the pistol was cocked, the safety was put on half-way and the trigger pulled, then when the safety was pushed completely forward, the pistol would go off. I tried 12 ways til Sunday to try and get the three Mark IV pistols I had in stock to do that to no avail. The two that were bought by customers were sent back to Ruger to install the new sear and safety plate, but mainly because the customers wanted that extra FREE magazine for doing so. I kept a Mark IV Competition Target and it remains, to this very day, just as it arrived from the distributor. Never had any issues with it.
Many complaints from owners concerning the Ruger Mark IV trigger pull, as it arrived on some pistols, it exceeded 7 pounds for pull weight. Aftermarket kits are sold to replace the magazine disconnect parts and also provide a much better sear. These kits run around $140.00. Now, I don't think anyone who has spent around $560.00 for a Ruger Mark IV should need to add another $140.00 to get what they feel they need for a well defined pistol, so I'm working on improving the internal parts, or removing and replacing, only if absolutely necessary: