I really don't like pressure barrels, they leak far to easily and are prone to cracks/ruptures, i just use mine for racking to before bottling as it has a bottom tap, gotta echo what Spoc says, use plastic cola/sparkling water bottles, if you have 1 or 2 champagne bottles you could use one for the "grand opening" at a party and then do all your refills from plastic bottles. Also unless your prepared to inject co2 into your barrel to maintain pressure the champagne is likely to go flat pretty quick.