I just put a little lubrication where the manual recommends.
My barrel isn't Melonite finished, so I also make sure to have a thin sheen of oil on it, especially at the locking surface:
Every time I hear people say "a drop of oil," I hear the voice of George Harris (Director of the SIG Academy) in my head. He'd immediately ask you, "How much is a drop?" George's recommendation, which I've used with great success for years, is to put enough oil on the surface so that you can see it's oiled, and if you touch it you leave a light fingerprint in the oil. Any less and it's not lubed; any more and it's probably just going to run off the gun.
For extended shooting sessions you might want a little more lubrication, but I haven't found my M&P to need it. Remember, excess that comes off/out of the gun was just wasted oil.
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