From http://www.dailymail.co.uk/news/article-2859301/ISIS-s-latest-killing-machine-10-foot-sniper-rifle-fire-bullets-three-times-size-normal-gun.html

It’s so big that it has to be supported on two tripods and fires ammunition that’s three times the size of standard rifle ammo.

An Isis terrorist has been photographed aiming a 10-foot long sniper rifle out of a flat window in Kobane.

The fearsome weapon fires 23mm calibre bullets, far larger than the standard size.

First off, I’m not sure I agree with the labelling of this weapon as a “sniper rifle”. I’d call it more of an anti-armor gun. In any case it highlights the point that at the end of the day, a “gun” can be a tube that suggests a direction for a round to fly…

This is a mighty big tube, and a pretty big round.  I’d think that aiming it accurately would be an issue.  Any current (or former) cannon cockers want to weigh in?

Thanks to Greg A. for the submission.