Now we're getting more specific. Misfires like the ones you describe indicate ammo problems, or perhaps a very unlikely mechanical problem.
Addressing the ammo question: If it doesn't shoot well with fresh Federal copperclads or Lightnings, Winchester HV (Dynapoints) or the index 1522 Remington solids with the gold bullets, you probably have a mechanical problem. (all of this ammo is bulk pack stuff that shoots well in my guns.)
Soft ignition could be caused by: a) A weak or weakened mainspring...unlikely in a NEW gun; b) lots of crud in the mechanism, impeding hammer fall; c) the dreaded 'other'. So you might try a more thorough degunking, and/or a replacement of the mainspring (count the coils on the one presently in the gun: there should be 28 of them.) Both the cleaning and spring check are well within at-home capabilities, no factory return required.
You just might have a firing pin that's on the short side of spec, which would cause light hits on some thinner ammo rims. This is one of those 'other' deals that mean a trip back to Ruger to correct.
Since the gun shoots well with WMR ammo, I'd suspect that all the long rifle stuff you have tried is pooped. Keep trying with fresh ammo, maybe from a different shop (you never know under what conditions ammo has been stored before you buy it)..you can spend a lot on rimfire ammo before you begin to approach the cost of UPS' or FedEx'ing the gun back to Ruger.
Has the gun shop source of the pistol/ammo been any help? Perhaps not, if you got it at a Wally World sort of place.
I sure hate to hear someone is having trouble with one of my favorite fun guns!