I have a Mark III slab side competition model. I don't know about the Mark I and II, but it is probably the most accurate out of the box next to a Browning Buckmark. It is a heavy gun and I put a 2.5 x 8 scope on it. A little pricey, but heck, it's a Ruger and totally worth it.
I know that the Mark I and Mark II magazine buttons (the thumb button that holds down the follower to load the mag) are on opposite sides of the magazine and that the original Mark I held 9 rounds, and I suspect that there are internal differences as well, but have never played with the innards of a Mark I.
The Mark III changes (from Mark II)seem to be mainly driven by lawyers-there is a magazine disconnect and a loaded chamber indicator.
I have installed a Volquartsen Accuracy Group in a Mark III 22/45 that seemed to work fine, so I think the mechanisms of the Mark II and III are the same beyond that.
The Ruger MKI slide lock and safety are the same button. Thus you can not pullback the slide on a MKI if the safety is on. (You have to have the safety off to eject a live rd). The MarkII has seperate buttons, one for the safety, one to lock the slide back.
Magazines, the MKI held 9 rds and the bolt would catch on the follower. It did not lock the slide back. The MKII held 10, and would hold the slide back on the last rd.
Here is a MKI..has only one button, a MKII will have 2 seperate buttons.
This is one of the best postings I have made, since I have learned a bunch here.
Everything the guys have said about the Mark I is "spot on." One button for slide and safety, 9 shot magazine, no interlock for open bolt on the last round.
Just IMHO, not a straw's worth of difference that is of any importance to me.
I really like my Mark I. Most of us don't need "lawyer" gadgets. Maybe some enterprising company should come out with "lawyer targets." We would have some scissorbill jerk with a suit and tie, wearing horn rim glasses, carrying a briefcase.
Thanks so much for these informative replies. BTW, I have had my Mark I for about 35 years and put as many as a couple of thousand rounds through it. Never found the need of a second .22 pistol. Shot a few rabbits with it. My version has the 6-7/8 in. barrel. Some have the 5 in. bull barrel.
The Mk I was not relieved by the grasping area of the bolt like it is on the Mk II and Mk III; the reassembly of the Mk I and II are identical; the Mk III is very different as you have all the added "safety" features ie. the magazine disconnect safety, the loaded chamber indicator, etc
Left has the cut in front of the bolt, right is the Mk I style
Here is a MkII 512T and a MkIII with the LCI removed
I had a MKI and a MKII. I liked the bull 5" barrel on the MKI, and was not so fond of the long tapered barrel on the MKII, so I sold that to a woman who liked it. The differences didn't mean anything to me with the one or two buttons. The earliest MKI magazines did not have a follower that came up high enough to hold the bolt back on the last shot either. They started making them a few years later.
I've got a MkIII target with the 6.88" heavy tapered barrel, which I don't think Ruger offers anymore. I love it, it shoots great and it really like the looks and feel of it.... And the trigger from the factory was really light and smooth!
Every time someone calls a magazine a "clip", God kills a kitten
I have a MkI Target Model with the 6 7/8" tapered barrel, thumbrest stocks, wide trigger, target sights. The safety functions as a slide release. I don't know that it's intended as such, but with the slide back you can put the safety on and it will hold the slide back. Slide the mag in and push the button down - slide comes forward and chambers the first round. The magazine base is chrome, the trigger is chrome. The printing on the red box and the cardboard shipping box that holds the red box indicate January 1973.
My MkII 22/45 is also a target model. The front button works as the slide 'release', independent of the safety. The wide grip on the 22/45 is the trick to change the grip angle from the original imitation of a Luger to imitating the 1911. The mag goes in funny - not parallel to the sides of the grip like you would think.
The MkI is my second one. If anyone wants one NIBOS, check out Baker Brothers Sporting Goods in Bucyrus, Ohio. I don't know if he has a website, but I doubt it. He does have a phone, though. I got this one from Brad a while ago and he had about half a dozen others in the safe. Pretty much let me take my pick. Of course I also paid about 6 times what I did for the first one I bought in 1968! That's one I shouldn't have sold, but you know what they say about hindsight.
Sounds like you own the same model I do, Teach. I traded a standard Mark I plus cash to get it. It's the pistol I shoot most often because I use it to "warm up" and get my eye in before I shift to whichever centerfire I brought to the range today.
To add to all the differences between the MK I, II, & III that have already been stated, the MK III's have the mag release on the left side of the grip. Where the MK I & II have the mag release on the heal/base of the grip.
I have a MK II Gov't Target and I really like it. I received it when my Dad passed away a few years ago and it will be passed on to my kids when I'm gone.
I bought a new Mark 1 in 1976. Everything these guys said about it is correct except the mag capacity. Mine came with two mags. One held 9 rounds as everyone here mentioned, but the second held 10. The 10 round mag would not lock the chamber open after the last round. The nine round would.
I now own a a Mark III 22/45 Lite. Great gun, but I really miss my MK I!
I own a MK 3 standard and 2 22/45 MK 3s (1 bull barrel; 1 slab sided). All the previous posts are great and accurate. Mk3s have a magazine disconnect safety and alot of printing on the gun which I am not crazy about but that's Ruger.
I like the 22/45's because the balance to me is closer to a 1911 but the grip is thinner. The only drawback (unlike the standard or other models) is the grips are integral and cannot be swapped.
My favorite for shooting is the slab side which has excellent balance, trigger, and sight picture. I too use it as a "warm up" and training pistol. It has tends of thousands of rounds through it and has never been apart (HAS been hosed down with degreaser, lubed and had a bore snake through). The gun will get less accurate after a few hundred rounds until a bore snake gets run through the bbl but is more than acceptable. I wish they still made the slab side version.
The guns are inherently VERY accurate and very reliable. Mine (like all semi-autos I own) love the Federal bulk champion and blue box 550s. I find the federal bulk hard to beat--even over more expensive ammo--in these guns. The 5" bull barrel claimed a 125 yd. kill on a groundhog, but there was a great deal of luck and surprise involved on all ends--and it was a once in a lifetime (or at least several decade) type of thing.