WD40 is ok. It doesn't last very long though.
I have been using Break free CLP, which is technically gun oil, and it lasts longer. The advice comes from the SCA, and this blog post in particular. Maintaining your Plate Armor (in a modern fashion).
Most recently this was mentioned in the sub 2 months ago.
Eezox may be slightly better as far as corrosion resistance, but CLP is almost half the price for the same amount. It works perfectly fine, I used it in the military and have used it on my personal weapons for years.
There. Just saved you $29. That's over 250 rounds of ammo at today's inflated prices.