Probably best to let a gun smith take a look at it. The barrel and cyclinders will need to inspected for rust.
If it's chambered for .22 mag don't use LR in it. The LR casings are not quite as big around as the magnums and will split when fired. You might also have a "squib" like I did when I borrowed a Colt SA that we thought had a .22 LR cylinder in it (it was a magnun cylinder instead), to take my handgun safety course.
A "squib" is when the bullet doesn't make it out the barrel and gets stuck.