Wd40 will penetrate your stock and ruin it-get it off QUICK! Best thing for stock is a good stock wax on the finish. As far as the metal,in time it will form a gummy buildup that's hard to get off-both inside and outside. Inside action it will attract dirt,dust,powder residue,etc to cause malfunctions after awhile. Use a good strong cleaner and then a good rust preventive.