Not so. Though this isn't the case with the page you linked, many other pages are locked and moderated very strictly. Additionally, any sensible person should check the references on information, hence the [citation needed] meme.
Even the Wikipedia page about "Editing" is locked. A study was conducted years ago measuring the accuracy of claims on randomly sampled pages and found it was more accurate than Encyclopaedia Britannica (Giles, J., 2005). VPNs are prohibited from editing, IP logs are stored on servers, and "talk" pages document each topic's editorial change (quite interesting for some topics).
en.m.wikipedia.org
Now I don't know anything about guns at all but you're both right apparently:
The 9mm cartridge has been in development since 1901 and is now available in several different bullet grain weights with unique properties.
blog.cheaperthandirt.com