Just putting this here so people, especially me, won't need to search announcement threads for it.
Here is the table of Amplification showing the % of improvements from your equips.
+1 amplification is 100% success and you won't lose your weapon, beyond that is random and you may lose your weapon, lose durability ( break your weapon to 0% repair ) or get downgraded if you DON'T use Sign of Imperishability, though if you use Sign of Imperishability this does not mean your amplifications will a
you can add chances too i once had a chance to contact devs asking about chances of amping andthey said
thier answer was this i think but im not sure maybe i forgot i wish i recorded it
but im sure about +1,+2,+3,+4,+5,+9,+10