UTG L96 barrel question

Well my dilemma is that I want a tighter bore barrel than the stock barrel and I'm sitting here trying to find one that will fit the stock utg L96 hopup and I cant seem to find one (or atleast be sure) since I'd rather not buy a barrel just to realize it wont fit my stock hopup. I know I could solve this problem by buying a PDI hopup but Im trying to find a way around that due to personal preference