Actually if you google "non-toxic gun oil" you come up with a lot of brands that are not only non-toxic but also biodegradable. I wouldn't personally want to use even the biodegradable stuff as lube, but the brand you linked to says right in its ad copy that "[d]uring Operation Desert Storm, Marines jacked off with actual military-issue gun oil while hunkered down in the trenches of Kuwaiti battlefields." Which shows if nothing else that guys will put just about anything on their dicks in extremis, whether the thought of it makes me cringe or not.

Glad you liked the fic anyway, though - thanks!