As others have said there is a trick to field stripping/reassembling the Ruger MK series.
Read and follow the directions. You know that little book they put in the box with the gun, or they'll send you one for free if you bought a used gun that didn't have it. BTW. You can find it online also. If you read and follow those directions, you'll have no trouble. If you have trouble, it's because you didn't follow the directions. I know because I didn't follow them. I wanted to do it MY way, not the way the guy who designed it, built it, and literally wrote the book on it said to do it.
Although, I must admit, nowadays, I don't bother. I just spray it down with Gunscrubber and put a couple of drops of oil back on it, here and there.
Any one of the three Rugers, MK I, II, or III, or the 22/45. They're all good guns. I've owned all of them at one time or another and never had a minutes trouble with any of them.
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)