[SBE II - Light Load Cycling problem]

When you "cleaned it completely", did you remove the stock and inspect the recoil spring assembly? If not, that's where I would go first.

 

+1 My SBE2 started having issues with 3" shells- Bolt was sluggish. I cleaned the recoil spring assembly, removed a few pieces of mashed up reeds, and applied a light coat of CLP. Bolt is now super slick again and cycles perfectly.

[Benelli M4 -- Magazine Tube Polishing]

A dry teflon lube (PFTE) will work well and not corrode anything. You can pick up a spray can of it at most home improvement stores. It sprays on wet and dries to a white slick film that won't attract dirt.

[Benelli M4 -- Magazine Tube Polishing]

Good idea to polish the tube, but you may want to use something other than steel wool as the abrasive. Steel wool will imbed itself in many metals and rust even if used on a non rusting surface (like aluminum). I polished some aluminum, stainless steel and titanium parts on my dirt bike using steel wool and all showed rust within six months.

 

Using a high #automotive sandpaper (1000-2000) in sequence will give good results, followed by Flitz or Semichrome polish. Also dry teflon will reduce friction and not attract dirt or grit.