Try tapping the boltstop with a small mallet.
I did it the easy way and took it to the gunsmith. I found out that I wasn't the only one having that problem. :)
Tis a bear to do .....I have a few Mk I’s and use a dunk cleaner these days ........ I hate to take it apart .
http://www.youtube.com/watch?v=Yvxf1H6YYII
The videos show the trick, I think my method was to reassemble upside down.
It sounds like the hammer may be in the wrong position, remove the bolt stop, and seperate the receiver from the lower, then start over again, making sure everything is in the proper position as you assemble, be sure the firing pin retainer pin is in place, then follow the instructions carefully when turning the gun upside down. They are tricky but with a little practice it gets a little easier.
Assembling and disassembling the MKIII is what caused me to choose a Buckmark Hunter over the Ruger.
The video posted above looks like the ‘trick’ that I was told about before I bought my Buckmark. Either pistol is a tack-driver and feed any type of .22lr.
One of my friends bought one. I disassembled it in front of him and challenged him to put it back together. He couldn’t. Hours later he was still working on it. I took it from him and assembled it real quick. Then disassembled it again and handed it back to him.
More cussing and trying, then he found out the secret. When you assemble it, as you put in the handle latch and vertical crossbolt, TURN THE PISTOL UPSIDE DOWN! The latch will then close.
I bought my first Ruger auto pistol in 1968. It cost $45.00 brand new in Little Rock, Arkansas.
You got the Ruger with all the extra "lawyer installed" parts.
I have two of the earlier versions, my advice is get some spray version of Gun Scrubbers, some small bronze brushes or use a regular cleaning kit brush and get a small air compressor, spray, soak, scrub the bolt face, the chamber, clean barrel normally but be careful at the crown, get nylon coated or brass cleaning rods.
And use compressed air to blow all the junk out. They are the most difficult to field strip, of course practice can help you find the proper angle of attack. Spray some CLP at the moving parts and if necessary use more compressed air, wipe off any excess oil.
My .02 cents.
The video in Squantos' post #10 is quite helpful.
I don't disassemble it any more.
Now I simply use a .22 caliber pull-through bore snake, Q-tips dipped in Hoppes #9 powder solvent, CLP, and Remington Rem Action Cleaner.
The Ruger .22, beginning with the Matk I, has always had a reputation for being a bear to strip and reassemble. It can be done, but it’s far from easy. Be patient, and good luck.
Sweet shooter, though. Nice ergos for my hand. YMMV.
I own 5 Ruger Mk IIIs which I use to train college students in pistol shooting (Thank You NRA!). So, I am very experienced at cleaning them, and they see a lot of service. Two hints. 1) Read the instructions every time on re-assembly, particularly the part about holding the pistol upside down. That’s the secret. The video is likely very good, but I haven’t seen it. 2) Save money by cleaning with brake cleaner ($3.50 at your local auto parts shop). I only take them down once a year because the brake cleaner is so easy and good. Follow with CLP.
Easy trick. Do the final assembly UPSIDE DOWN. The little whammerdooddle stick has to hang down to stay out of the way. Otherwise, if assembled rightside up, it will snag and get stuck on the whatchamacallit.
If you don’t own a Ruger .22 pistol, this will make no sense. If you do, it will.
Let me guess, you got the 22/45 version?
I pulled my hair out getting mine apart and never could get it back together. Paid a gunbroker and bought a bore snake.