Cleaning question?
 

When ever I clean my M&P 40 and wipe it down with oil it start to get oil spots after a bit. It goes away when I wipe it down with a clean cloth, but always comes back.

Does anybody know what causes this?

What kind of oil are you using? Are the oil spots around seams?

I'm using hoppes oil. The spots are all along the side of the slide. Both sides

.................

I put oil on a cloth, then wipe it down to get a good sheen. Then I wipe off any residual oil. Leave it sit for a bit and starts to develop oil spots

Use less oil...although it seems like there is no residual oil after wiping it down, there is a very thin layer that "pools" into the spots you are seeing. Try wiping with a dry cloth after applying what you think is not enough...a little oil goes a very long way on non-porous metal.

Alright I'll try that next time I clean it

Hoppes is a heavy oil that is hard to wipe down. I use slipstream weapons grease on the rails of semi-autos, Remoil on the exterior of the barrel, and heavy oil such as hoppes on the hammer/trigger assembly.

Make sure to remove as much oil as possible from the rails before applying any type of grease. Oil turns any grease into goop.