The Mark I is safe to dry fire same as the MK II or III. The firing pin stop has been part of the design since day one. According to Rugers FAQ's, all Ruger rimfires are safe to dry fire.
I've got two Mk I's, and a Mk II now. I've owned a couple of Mk III's. I can't really tell that one is better than the other. The II's have a couple of features that I like, but they're not that big a deal. The III's have a few features that I don't care about, but they're not deal breakers either. I just look for the best price.
I believe only the target sighted models are properly called "Mk I"'s. The fixed sight tapered barrel guns were simply called "Standard Automatic". Since there hadn't been any changes planned in the beginning, there was no need for a "Mark" number. The adjustable sights were the first change. Most people however refer to anything pre Mark II as a Mark I.
For God so loved the world, that He gave His only begotten Son, that whoever believes in Him should not perish, but have everlasting life.
John 3:16 (NKJV)
Last edited by CajunBass; January 30, 2013 at 08:52 PM.