I have been having good results with MicroLubrol - a 100% Silicone oil.
I put a few drops on the bolt head lugs and wipe with a cotton rag. Just a very light coating.
The rest of the metal gets an occasional wipe down with Birchwood Casey Sheath (was formerly Barricade) that is a protectant oil.
I use liquids - not sprays.
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