IMHO, the best version to build is the Mk. II, or if you want the 22/45, a Mk. III with Mk. II internals, or Volquartsen.
The Mk. I does not lock the bolt open on the last round.
The Mk. I safety does not permit you to cycle the bolt with the safety on.
The Mk. I magazine is slightly different and holds 9 shots. Later marks hold 10.
A Mk. I can be updated to a Mk. II except for the scalloped receiver cuts. This a fairly simple to do for the advanced tinkerer. There's a "how-to" thread from about 14 years ago posted on this site.
The Mk. II upgraded the design to include last round hold open and a safety that permitted unloading the pistol with it on.
There is also scalloped cuts on the receiver to make grasping the bolts ears easier.
And a new 10 shot magazine.
There was also a 22/45 version with a polymer frame that was a step in the right direction, just ugly.
The Mk. III featured a loaded chamber indicator, and a magazine disconnect safety, both of which are of dubious value IMO, and they greatly complicated the disassembly/reassembly procedure. Plus the LCI caused its own issues with feeding and the mag disconnect prevented the mags from dropping free of their own weight.
If you know and follow the
4 Rules, you don't need an LCI. If you don't know and follow the
4 Rules, you probably won't even look at the LCI anyway.
The best part was Ruger redesigned the 22/45 and got it right this time. Eventually, they even added 1911 grip panels that topped off the design. The good news is you can replace the Mk. III parts with Mk. II parts and get rid of the dubious features. If you want a good 22/45, this is the best way to get it.
The Mk. IV is an attempt to address all the complaints from folks about the Mk. III and its take down. The upside is its easier than ever to take apart and put back together, but this also means no backwards compatibility with the previous marks.
Ruger abandoned the Mk. III LCI and redesigned the mag safety to permit drop free. So, one step in the right direction anyway.
They also redesigned the safety changing it from a sliding button to a lever. And it's now ambidextrous.
Ruger has had a recall on the Mk. IV. If you buy one used, you need to see if the gun has had the recall fix performed on it. Here's how to tell.
ruger.com
Under the title of amusing anecdotes:
Many years ago, back when things were B&W, years before the internet and quick and easy looking things up etc., I had a friend who came into my parts store and asked if I knew how to put a Ruger 22 pistol back together. It seems that he bought this pistol used and of course the owners manual didn't come with it. He took it apart to clean it, and then couldn't get it back together properly. Every first time Ruger 22 auto owner has experienced this.
So I go over to his house and he has the "box-o-parts" on the kitchen table. He pushes the box over to me. Then his 4 year old daughter comes up to him with some urgent to a 4 year old matter and he turns to deal with her. When he turns back around maybe 20 seconds later, I hand him the assembled pistol. I wish I had a picture of the look on his face. He says "I spent an hour trying to get this back together and couldn't figure it out". So I had to take it apart again and show him how to do it. It's not hard, but if you've never seen it done and you don't have the owners manual, most have trouble.
Those that I know that own a Mk. III say it's a royal PITA to take apart and clean, so most don't. Fortunately, the Ruger will work even when neglected.
