I had such low success with it I didn't even try to use in PKs. I once did a highly scientific experiment in the felar village, trying to find what elements got my success rate up:

big high hitroll: marginal improvement
wielding big heavy mace: no difference
wielding little dagger: no difference
enlarged/reduced: no difference (aside from not being able to if too small)
hiding: no difference

All in all, the best weaponbutt success rate was 58%, with a hitroll over 30. With a hitroll of 15, it was like 53% - could have just been rng for all i know - i only did one run around the pile with each variation.

poop on weaponbutt.