Dis-assemble the bolt, and thoroughly clean it, especially inside.  Use a good light to verify inside is squeaky clean.  Clean all parts, lube lightly, and re-assemble.  Might be some gunk inside.

If for some reason you cannot dis-assemble the bolt, flood it several times with brake cleaner from the auto parts store (mind the fumes), and hit it between cleanings with compressed air.  Lightly oil afterwards.

Last resort:  Submerge in a good degreasing solution overnight.  Next day, agitate several times and re-submerge between agitatings.  Lightly oil afterwards

If this does not fix your problem, then the issue might be either with the firing pin protrusion, or maybe even the headspace.  Contact Ruger.  www.ruger.com If you must send the rifle back to Ruger, take a minute and determine which, if any, parts can only be obtained from Ruger .  This is the time to order some fitted spares for the future.  Plastic bag the spares, and drill a hole in the buttstock big enough for them.  Replace butt stock cap, and you'll never lose them.