Some firearms require grease. Some of the early all-stainless pistols would suffer slide and receiver rail galling with oil, so grease was required. White lithium grease has a useful temperature range of about -40F to 360F. I don't see me holding a pistol that is outside of these temperature ranges, so I do grease slide/receiver rails.

Revolvers need less lubricant and typically only need a tiny bit of oil. Most of the oil on my revolvers is on the exterior of blued finishes, remarkably little on interior surfaces.

Regardless, Max 503 has made a very good point about routine care of firearms.

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VCDL, GOA, NRA