Or, "Help! I Field-Stripped My Ruger .22 Pistol, and Now My Wife Is Pointing At Me and Laughing!"
The Japanese lost WWII because we fought our way across the whole Pacific before they could assemble their pistols. Shortly after the war ended, a maniac named Bill Ruger designed a .22LR knock-off of those same pistols. It looked a bit like a Luger, but it was a mostly Japanese design, so he called it a "Ruger", to make fun of the Japanese accent. That's why their agents killed him, later on. That was a damn shame, that they got to him before I did.
The original pistol is now called the Ruger Standard, because it had no other name. Later models were called MK I, MK II, etc. They are very accurate, if you throw them overhand. Mine is a Standard made in 1954, according to Ruger's serial number history. These pistols are not so hard to take apart, but a popular self-administered IQ test among fools like me is trying to put the miserable things back together. It took me less than three days to figure out, even counting that break I took after the sledgehammer incident.
So, there's a tricky spot that you hit in putting the Ruger .22 pistol back together: The mainspring housing won't go in, and it won't go in, and then finally you get it in — and then the bolt won't pull back. If you Google around, lots of people have this problem. There's advice here, and there's a YouTube video that I found helpful as well. I did not find the vendor's manual helpful with this problem. It's like the Duff's Device of firearms maintenance or something.
The way you get it back together is by correct positioning of the hammer, and of a piece of metal attached to the hammer by a pin. The metal thing seems to be called the "hammer strut", or the Stupid Flippy Thing. The material linked above didn't get me over the hump with that. Finally, I got it by trial and error, repeated it a few times, and took pictures which I hope others may find useful.
First picture: The hammer in the correct position. It can be in a lot of positions, and it was not obvious to me which one is correct. The hammer is the silvery, triangular metal piece sticking out of the top of the frame. It's actually trapezoidal, but you can't see the whole thing from this angle. You may need to pull the trigger to get the hammer into this position (this should not need to be said, but DO NOT pull the trigger unless the gun is UNLOADED and DISassembled, as shown in the photograph). Click to enlarge:
Second picture: The same thing, viewed from behind. Near the top of the rectangular hole in the back of the grip, you can see a vertical shiny metal piece just above a horizontal blued pin. The vertical piece is the hammer strut. It is attached to the hammer by a pin on which it swings freely, and it hates you. It is just sitting there, a tiny piece of metal filled with hate. This photograph demonstrates where it should be at this stage of things. Its point is resting against the wall of the magazine well, just above that cross-pin. The hammer strut will have to flip out of there before we're done, so you'll want to have the hammer positioned so it isn't jamming the hammer strut in behind the pin. Just let the hammer strut's tip rest a little above the pin. Click to enlarge:
Put the hammer in the position shown above, slip the bolt back into the barrel/receiver piece, and carefully put the barrel/receiver back onto the frame without disturbing the hammer. Hold the frame upright the whole time. That part's easy.
Next, turn the pistol on its side without disturbing the hammer strut. Put the mainspring housing in, and drive its pin up through the bolt, all while keeping the hammer strut where it is, with its tip against the mag-well wall just above that cross-pin. Once the mainspring housing pin is inserted fully, tilt the gun so the hammer strut flips over onto the mainspring housing. If the hammer strut won't go, flip it with a pencil or tweezers or something.
The last picture shows the gun inverted, with the mainspring housing pin in place, the mainspring housing itself lolling out of the grip like an obscene steel tongue, and the hammer strut flipped onto the mainspring housing, where it ought to be now. The tip of the hammer strut is about dead center in the red circle; not a great picture, sorry, but it's the small shiny bit. The horizontal shiny line at the top of the red circle is the cross-pin mentioned above. Click to enlarge:
You should now be able to close the mainspring housing and draw the bolt back all the way. If the bolt won't come back, take it apart and try again. If the mainspring housing levers its pin out of the receiver when you try to close it, you've got the hammer and/or the hammer strut badly mispositioned.
Key points here: Hammer angle, picture 1. First hammer strut position, picture 2. Final hammer strut position, picture 3.
Good luck. God bless. I am not responsible for anything you do, think, say, believe, forget, remember, or neglect.
If there are any errors or omissions here, a civil heads-up about the matter would be very welcome indeed.