Benjamin’s Parrott guns were rifled for greater range and accuracy. So were the 3-inch bronze and steel cannon of Parker’s “Boy Battery.”
Both types of cannon were new, and also not so easy to make, according to these 1860 newspaper articles by the political radical Engels (of Marx & Engels’ Das Capital fame) who had been a Prussian artilleryman before he became a communist:
“The manufacture of firearms, up to a very few years ago, was the most backward branch of modern industry. There was far too much hand labor and far too little machinery. For the old smooth-bore arms this might be allowable; but when arms were to be manufactured which were expected to have great precision at long distances, this system became intolerable.
“To insure the certainty that every musket should shoot perfectly alike at 600, 800, 1,000 yards, and every cannon at 2,000, 4,000, 6,000 yards, it became necessary that every part of every operation should be performed by the most perfect and self-acting machinery, so as to turn out one weapon the mathematical counterpart of the other. Deviations from mathematical precision, inappreciable under the old system, now became defects rendering the whole system useless.”
Which probably explains why the muzzles of some of the Boy Battery’s guns, captured at Harper’s Ferry by Stonewall Jackson, exploded. Although it could also have been caused by their defective Confederate ammunition.