How to break a horse's jaw? (part 2.)?

This is the section for horses that are alive, not the weapon section. None of us would know.

Any reason you need to make weapons in the first place?

To be fair there are a few better wording choices you could have picked. The way you have it worded now made me think, and probably a bunch of other people, that you wanted to say, go out in a pasture and crack a horse across the face with a sledge hammer to break his jaw. So you can clearly see why someone would get a little upset about that. Good wording is your friend. Now, since you have the jaw bone (which is different than wanting to break a horse's jaw) I would imagine the best way to break it would be with a hammer and chisel. Or, I mean you could probably just give it a good whack with a sledge hammer and break it. A saw might be able to work too, but I dunno.

The Y!A horse section is actually a very good place to ask off-the-wall questions, because so many of the people here have their heads attached firmly (unlike your jawbone). Indeed a hammer and chisel would do well, or more properly a stone axe. I'm not really up on the techniques for making stone axes, or for sculpturing jawbones, but if you experiment for a while you may learn enough to teach us all a thing or two. I would bet that having a properly shaped anvil under the bone would allow you to put the blow in just the right spot. Be careful not to hit your thumb with the stone axe, but if you do, then immediately drop it on your foot so that you forget about your throbbing thumb.