My daughter is younger and smaller than my son, but in any "fun sibling violence" situation she just doesn't stop hassling until she thinks she's "won" or us parents have to intervene. They never really come close to even danger of the spilling-blood-kind of physicality, but my daughter constantly surprises me with what punishment she's willing to risk just to try and "get the last one in". She's tougher than him.

The "gun as solution" psychology is definitely a large part of the problem.