Many Model 1842's (and earlier muskets) were converted to rifles and the issue ammunition was a .69 caliber "Minnie" ball, not "buck and ball". The ammunition manufacturing records indicate that while "buck and ball" was preferred early in the war, the "elongated ball" (Minie ball) showed a clear preference as the war went on. For example, for the quarter ending 30 Sep 1861, Allegheny Arsenal made 4,591,000 .69 caliber B&B cartridges vs only 1,174,000 E.B. rounds.
But by the quarter ending 30 JUn 1862, the balance had shifted to 809,000 B&B vs 5,683,000 rounds of E.B. And that was the last production of B&B by Allegheny Arsenal.