Mac- I thought it interesting as well. It is common knowledge that some barrels burst while being buttoned. This used to be common with the 1137 and annealed 4140 blanks used on some comercial muzzleloaders. Hall Sharon once told me of this. This fact shows the tremendous stress put upon a black when it's being buttoned.
: That said, the most accurate Bench Rest barrels today, are button rifled. It seems the best 1,000 yard match barrels are cut rifled, and the most accurate commercial hunting rifles have hammer forged barrels.