2/3 chance to broke? Oo WTF ! ...Everyone knows success rate is 2/3 & there is 1/3 chance of failure ! Next time try reading hints on loading screens !
Make sure your 3rd post on the forum makes sense.
AND over enchanting is more about LUCK than anything else. Sometimes I do +10 without breaking and sometimes I break at +4 ...while my friends are able to craft almost every time, I have failed 60% recipe's 9/10 times ...and I dropped the whole night heavy set on a 5x server on the same day.
If u use statistics, and try to calculate the chance of dropping a weapon per x mobs killed ...the probability will RISE with every mob you add. But, if something has a 1% chance to drop, even after killng 100 mobs (100% chance) u may NEVER drop it.
It's called luck, & it's not taught in math class.