Not all drums are created equal. Some are heavier than others. Depends on what you buy them for.
Regarding your implosion, the cylinder of a drum is very strong. A dent though, compromises that cylinder and will lead to an earlier vacuum failure.
Drums are not meant for any pressure or vacuum storage.
Several times now, purely for entertainment, I loosely put a steam hose in an empty drum (not pressurized). Get her good & hot, pull the hose and quickly replace & tighten the bungs. After the steam cools, it pulls a vacuum. Once the drum goes, it is very sudden. Just don't be handling the drum and get your finger caught in a crinkle!