To expand a smidge. When we acquired the new barrel it was dry, and had never been used. Bought it from another homebrewer who never got around to using it. To ensure it would hold up, he filled it with a citric acid solution and let it expand before we picked it up. We kept it like this until a month or 2 before brewday, then started pouring the bourbon in and rotating. We probably poured about 1.5 750ml bottles of bourbon in it total. About a pint of it didn't absorb so we just left it in. The barrel could probably handle ~12 gallons, and we had 13 gallons after brewday, but lost 3 gallons to trub, so 10 went in. We tasted it a few times over the 8 months until we liked it, and here we are.