FP10 is a very good lube and works well in cold temps. Any lube should be used sparingly when cold temps are expected. And, make certain your gun is clean when you start. The powder fouling, combined with oil, can act like tar in the cold, slowing the entire gun's mechanism down, even pumps.
I have a couple of friends who sprayed down their 835's with WD40, and then went hunting the next day when it dropped into the teens. The sludge from unburned powder, combined with the WD40, thickened up and kept their guns from firing. The hammer just couldn't hit the firing pin hard enough to dent the primers. Clean the guns of the sludge and they worked fine, even when cold.