Well it's been a couple of days since this was posted and no one's took a stab at it. I was hesitant to because I don't honestly have any solid information to give you. However in the 1980's which was the hey day of the long barreled semi auto assault weapons I recall several gun magazines doing articles on them and it was repeatedly stated a few places that one benefit of the longer barrel with a 9mm round was that it brought it close to the same class as a .357 magnum. I've always wondered if they actually chronographed the rounds to see the velocity increase and compared this to rounds from a .357 revolver (no revolver barrel length was mentioned) Or if it just sounded good to them. At any rate if anyone here disagrees or has better information I certainly have no argument to make. In fact any of you with an HK 94 or an UZI carbine and a chrony might be able to develop some interesting conclusions I'd like to see after all these years.