It took me a bit to understand how yours works, very clever. I like the concept. I am concerned about the washers holding up, as they are taking a lot of impact. Second, that is more of a flat puller than a cats paw you used. I needed the cats paw with the points on the tips to be able to get under the nail heads. The one I used had an anvil on the back of the puller that I used to hammer the cats paw under the nail head. Are you pulling the same type nails I am? Are you pulling from Corrugated tin? If you have a nail in a valley, can you get it?

What I really like is that you saved the cost of having to buy a slide hammer. Please let us know more when you've done more testing- ergonomics, was the mass enough, could it be improved...I know I was pulling some decently heavy nails and after 50 or so, I could feel it in my arm from slapping. Brad