Ruthie, not is the Ruger is chambered for 38 Special only. Any 357 Magnum Chambered revolver can fire both 357 Magnum and 38 Special whereas a 38 Special chambered revolver can only fire 38 Special ammunition. Cheers and stay safe!

If the GP100 is a 357 you can use any commercial 357 or 38 Special ammo with no issues if it is a 38 special gun then the chamber is to short to work with the longer 357 round

If your Ruger is chambered for 357 Magnum then yes the legend ammo will work fine. If it's chambered for 38 special then no, you can't shoot 357 Magnum threw a 38 special revolver. So if your revolver has 357 Magnum on the side of the barrel then yes you can shoot without a problem. Hope this helps.