Alocksly: I'd be tempted to use small size steel or lead shotgun pellets to 'top'er up' when you head out for field testing. Bring an ordinary hatchet with you for comparison sake. I really don't know if or how much benefit there would be to the 'dead blow' feature when it comes to cutting or chopping wood. Could be it just keeps metal handle vibration transfer to the hand to a minimum. My experience with 'dead blow' hammers has always been good because you get no 'out of control' rebound stroke when striking something hard.
My thoughts too. I was going to pick up a bag of #12 lead birdshot from the gun store later today if I have time.