Right on top of the hammer is a rocker switch that will move the selector from centerfire (forward) to rimfire (rear). If you look at the breechface you will see the two firing pins.

Jet ammo is readily available on line. Reed's Ammo has it as do several other manufacturers. It is best to wear both plugs and headhone type hearing protection as the muzzleblast is not only loud but a very high frequency...

To shoot standard .22 rimfire ammo just put the rounds in the adapters and place them in the chambers. Then switch the selector to rimfire and shoot. Eject the empty adapters and take the empty .22 outs with a fingernail or small piece of coat hanger.

Serial number indicates a 1962 vintage gun...the first year of production guns had a screw in front of the trigger guard...yours should be a 53-2 with no screw...

Not sure what the going price is today but $1000 +- is what most people will pay for a clean one like yours...

Bob