I don't recall if the 550 firing pin will ding the chamber, but I seriously doubt that it will.
If it would, I'm sure it already would have done it by now.
That said, you can leave it cocked, which I'm also pretty sure it has been for 38 years or more.
Or dry-fire it without a snap-cap to relax striker spring pressure.
Pretty sure it has had that done a gazillion times too, just from running the magazine tube empty while shooting and snapping on an empty chamber!
They stopped making them in 1970, and if it still hasen't got a dinged chamber, or a weak striker spring by now, it probably doesn't matter which way you do it.
BTW: .22 chamber damage from firing pin inpact is pretty much a thing of the past with modern firearms designs.
At one time it was a major problem with cheaper / simpler rifles & revolvers.
It never was a problem with most higher quality designs such as the old Winchester 1890/06/62A pumps, S&W, Colt, Ruger, most Remingtons, etc.
That's not to say it's a good idea to dry-fire most .22's a lot, but it probably isn't going to cause any damage if you do so once & awhile.
rcmodel