User blog comment:Xanneer/PHYSICS!/@comment-24911350-20140531000733

A 30-45 degree spread, down from the 90 degree one now would actually make a world of difference, and be much more realistic for a shotgun. It being a shockwave rather than a bullet or shell was what was killing you on that, but the same thing means it's also affected much more by changes on the back end.

I wont get into the specifics of the math, but basically, cutting the spread in half to 45 degress cuts the recoil down to a quarter, which should be within that huge margin of error for RWBY-ness.

And to answer your question, they're directed upwards by recoil because the force is coming in above their center of mass, and that of the humans holding them. It's like a lever, the person's hips are the fulcrum in the center, and the recoil is the load on one side. It doesn't really go upwards so much as that it applies a force that makes your body want to spin in a backflippy direction.

You'll see that for large, anti-material rifles, users actually sit quite a bit back from the weapon because they can't handle the recoil against their bodies, and that's from what's still a relatively small amoutn of lead, whereas a shockwave acts like a literal wall of lead.