Does that means it's true? I highly doubt it. I wasn't alive in the 60s, but I've known a lot of Marines in my life. I was in the Army myself. I've known people who were Marines in Vietnam. I've never known anyone who ever operated a rifle who would interpret a claim this way or belief a self-cleaning rifle was a possible thing.
But unfortunately, even if you are personally an expert, Wikipedia doesn't let you come in and tell a page it's wrong. You have to publish your knowledge in an authoritative archival source and then it can be cited. I get that it can be frustrating as a subject-matter expert, but I don't know what better sourcing and citation rules an encyclopedia can have. They don't internally litigate the validity of a claim. They define what outside sources count as citable and then trust those sources.
Hell, I experiened a fairly stupid version of this a few months ago. I edited the page for Slayer's Reign in Blood in the section for pop culture references, adding a mention that Angel of Death was used in the Leftovers when Nora pays a prostitute to shoot her and uses the song to cover the gunshot sound. I linked to an episode summary on another wiki and that got deleted because apparently Wikipedia doesn't allow other wikis to be cited as sources. Fair enough as a general rule, though I think it doesn't make sense in this context because Wikipedia has episode summaries of television shows that don't cite sources at all. So I just removed the cite and linked to HBO's home page for the episode and that stuck, even though it doesn't have a description and you'd have to actually watch the episode to confirm I'm not lying.
But hey, whatever, rules are rules. No rules are perfect. Courts get it wrong sometimes, too.