Hugh,
Attached are two pictures of Spam cans, Russian Wolf manufacturer, I buried in 2009. You can see the difference of the one I repainted and covered in grease at the time of burial and the one left as bought. All ammo was fine inside of both, even though one rust spot did make a pin size hole. I re-canned them all. The ground was moist most of the time. Ammo was steel case. Thanks for the website. – W.W.