I wonder how many will mash a finger this week trying this . Thanks for posting Ben. I believe several references I read have mentioned holding the point in a piece of leather to protect the hand. I wonder if it also aids in holding the point more firmly in the grip. I will be giving it a try also...
Here is an interesting clip on youtube of a similar technique. I mention similar because it looks like he is striking the end rather than in the palm: https://www.youtube.com/watch?v=CfQUFERvPxI
The guy that owns the Youtube account, that KnapYucatan guy, he is just awesome. Oh, wait a minute, that is me!!! Ha ha! You found my Youtube account.
As for the leather, you do not always need to hold the point super firmly. I have made more hammerstone made overshots then I can remember. But, I do not think that I am gripping the stone that hard, even when full overshot is made.
Also, I do not know what happens when a break is formed. I can feel things happening in the process. And, I can guide things. But, I don't know how it all works. I just see the effects. And, I learned to control some of those effects to some degree, by a feeling, and by special knowledge. But, that does not mean that I know what is happening. Maybe there are components of the break process that I cannot feel, and do not even know about.
One of the things that I have wondered is whether the stone needs to be able to vibrate when struck. And, if so, does over-immobilization impede vibration? And, could this be why a heavily gripped stone might be harder to flake than a more lightly gripped stone? I don't know, and I will not pretend to know. But, someone might know.
That being said, you should hold the points with leather if you are doing heavy hammerstone work. The truth is that a large flake can dislodge, and clip a finger tip, as it is flying away from your hand. And, if it weighs enough, and is traveling at a very high rate of speed, and it has a sharp edge, it could seriously injure your finger, or finger tip. On at least one occasion, I have had a flake come off, only to catch a finger tip, and put a cut so large in my finger that I thought I would need stiches (or at least Super Glue).