I think I can best describe this in a story...
The other day, a 40" long box showed up at my office. I noticed, with a smile, that it was some O-1 tool steel I had been waiting for. I lifted the box and became immediately concerned because it felt too light. Perhaps they had screwed up my order and sent me less steel than I wanted?
I opened the box to find the correct quantity of O-1 strapped to a long wooden board. I went to pick up the bars and was amazed at how heavy it suddenly felt. Just out of curiosity, I slid it back down and closed up the box and picked it up. Again, amazing light. Opened the box again and picked up the steel. Surely the steel alone was not heavier than the box plus the steel..??!?!
You can imagine the scene I was creating here in my office...
It really has a lot to do with perception.
Two objects might be exactly the same weight but feel radically different in the hand.
So, while a 16.5 WWII is larger than a 15" AK, because of the slenderness and balance, the WWII feels quicker in the hand. When you pick up a 15" AK, you can't help but start chopping the air with it. The forward weight just begs you to do it...
Someday, somebody here will get their act together and do a true side-by-side analysis of the two. Point-of-Balance, weight, length, handle length and thickness, feel, chopping, thrusting, etc.
Just, not me this time.
Dan