I believe the Ruger is a piston action and it doesn’t need as much oil as the typical gas action AR style rifle. I’ve still always kept an AR weapon with a wet bolt.
The SR 556 is the piston gun, the AR556 is the standard direct impingment version.
Either way, follow the US Army/USMC guidance and use a quality oil like CLP, ) or any of the multi-purpose lube/cleaners out there.
For temperate operations use a light coat of oil on the internals, a drop on the trigger mechanism pins and sear and that is about it.
Those who suggest that ARs need to be slopping oil everywhere in order to run properly just wind up slopping oil all over the shooter and it really serves no purpose. Once the weapon is fired, the excess either is burned off the “hot” components ( bolt tail and carrier inner surfaces, leaving soot and carbon to add to the mess.
or it is slung off negating any lube quality- the end state will be a light coat of oil ( defined by the US Army manual as a drop or two of oil on a cleaning patch).
In dusty environments, less oil is better- oil tends to gather dust, dust and oil create an abrasive. A dry dusty gun blows the dust off most components upon firing. In wet environments too much oil mixes with water and does nothing more than a light coat. In a cold arctic environment, oil can coagulate/thicken and impede function, LSA is called for (artic lube).
End state: Lube the way the military recommends- they have lots of experience.
An AR in proper order will run dry w/o negative effects.
A properly lubed weapon runs well w/o issue too.
Best,