Doubling is usually a sign that either too much filth has built up, preventing the trigger mechanism (or part of it) from working, or that there there is enough wear that the trigger is not able to reliably function as it is supposed to.
.22's are dirty, semi autos, even dirtier, and guns like the squibmans tend to get bought to run clips at a time off down range, so they tend to accumulate a lot of residue inside the action.
A good stripdown and cleaning is a start, you don't need anything fancy, just a couple clean(ish) cloths or even a roll of paper towels, an an old newspaper to work on to keep the oil off the rest of your stuff.
Dig around online, and you should be able to find a parts diagram if you don't have one, but it should not be a requirement.
Look for build-ups of mung and look for rounded off edges while you are cleaning each of the small parts.
A little dab of oil at each moving pivot should be all it takes.
Cheers
Trev
