The two Firestorm .22 models I'm aware of are the FS22M (matte finish) and the FS22DT (matte/nickel duo-tone). The finish is the only difference between the two, as far as I know.
Don't read too far into the single/double action business- it'll only get you confused! :oops:
I'll attempt to explain it in a simple fashion. Might not be 100% technically correct, but hopefully will shed some light on things for you.
Single action: squeezing the trigger does a "single" action- it drops the hammer. Think of an old cowboy revolver in the movies (called a single action revolver), where you have to cock the hammer before each shot. Your trigger squeeze performs only a single action- it drops the hammer.
Double action: squeezing the trigger does two things, a "double" action- it cocks, then releases the hammer. Think of your stereotypical .38 Special revolver- just squeeze the trigger, and the hammer is cocked, then released, firing the gun. Your trigger squeeze has just performed two actions, cocking then releasing the hammer. Hence the name "double action..."
Keep in mind that most "double action" handguns (revolver or semi-auto) can be fired in a "single action" mode by manually cocking the hammer. Then when you squeeze the trigger, there is only a "single" action left to perform- dropping the hammer. Some exceptions to this would be a revolver whose hammer is hidden under a shroud, or where the hammer spur has been ground down. Other exceptions would be a "double-action only" semi-auto. A Glock handgun would probably be the most familiar example, though their proprietary "safe action" might not be considered a true double action by someone who is into precise definitions.
Clear as mud, so far???
The Firestorm operates in the manner of what I would call a "traditional double action" auto pistol.
The first shot can be fired double action (just squeeze the trigger), or single action (cock the hammer manually, then squeeze the trigger).
Cocking the hammer manually yields a much lighter "single action" trigger pull, as you are not cocking the hammer with the trigger pull.
Second and subsequent shots are fired single action.
There is a decocker lever on this pistol, but my trying to explain that would leave us all in trouble...
Here are a couple of links that you might find interesting or helpful:
Gunblast review of the Firestorm .22Brief article from Firestorm websiteI have a Firestorm in .22, and it's a fun plinker. I paid about $225 plus tax for mine, about a year ago.
Hope this has helped, at least a little!