If you heard a bang, the tube got out of the tire. This happens most often when it gets caught under the bead during mounting. The 6" tear is also a giveaway that the tube was outside tire.

Consider doubling up on the rim tape thickness to give the tire a tighter fit. The tube may be less likely to find its way under the bead then.

You can use a 700C tube in a 24" tire. Just neatly fold over the excess length and jam it in there. You won't feel the lumps when riding, but after a few years the tube will perish at the folds.