Theoben Rapid S 0.20" Calibre.....

Without a barrel as it is faulty, and I am trying something first before I buy a new one, my friend is taking 30mm off the end and giving it an 11º angle on the end or Crown as it's called, hopefully this will put it right, if not then it gets a new barrel, and it's an odd caliber being 0.20" normally it's either 0.177" or 0.22", I just had to be different didn't I?