My apologies sam, i have never filled it to 4500, never got the chance, but on the bottle it states '465 bar' and just had a quick look on this thread: http://p8ntballer-forums.com/threads/air-bottle-im-a-little-confused.45575/Just incase you missed it
It was a team bottle and have been told it is a fibre bottle. All i can say i'm afraid