So, I know it's a sub-optimal alternative to silicon spray but it's all I'll have for a while. Also, it's going into a really cheap Crosman AEG SMG that I only use as my side weapon. The gun needs lubed pretty badly, but I don't have silicon. I only use it on the barrel, though it's possible some might get into the hop-up chamber. Then I clean it out with a pipe-cleaner.
How bad is this for my gun? It's only until I can get my hands on some silicon spray, and I'm not using it for my overpriced Dragunov.
As filletofspam said, WD-40 is for water displacement (hence the name WD). Also helps to break up rust and grime.
For lubrication I use 3 in 1 oil for most household things and all my firearms. Stuff works great!
WD-40's main purpose is to disperse water. It is a pretty good penetrant but is mainly solvent with only 15% light mineral oil. It is probably better than nothing but is not a very good lubricant.
The Prodessional Tool Box...contains 2 items:
1) Duct Tape - use if it moves and isn't supposed to
2) WD-40 - use if it doesn't move but is supposed to
My dad cleans his hunting rifles and shotguns with WD-40 ;)