509mm is abit too long, and i dont know if the standard cylinder is ported for a barrel of that length. iirc standard length of a CM16 is 360'ish mm
in any case what aspect of your gun do you want to upgrade exactly ... a TB barrel will only give you a mild FPS increase.
if you want range, use heavier bb's. if you want accuracy use branded bb's.
as for the hop, if your hop rubber is worn out, a standard G&G rubber is pretty good, or a TM rubber