For many years I have owned an 1842 Springfield musket. The lock is dated 1848, the barrel 1851 and a not uncommon arsenal match (or mismatch). I noticed right way when I got it that the barrel was pretty thick (and heavy) for a smoothbore, much more so than the barrels on an 1816 or 1795. I later learned that 1842's were made that way so that in the future they could be readily rifled and many, indeed, were in the 1850's. Recently I acquired another Springfield 1842, the lock dated 1846 and thought the barrel looked thinner. Since these arms were the first muskets to have completely interchangeable parts I wondered about that. Today I did a bit of measuring with a digital caliper I use in reloading modern brass cartridges. The interior bores of both arms were exactly 0.692 in diameter but the thickness of the barrels was different. The earlier 1842 did, indeed, have a thinner barrel, namely 0.079 inches while the later arm did have a thicker barrel, 0.090. Is this by chance? Is there some significance to the difference or just inconsequential manufacturing tolerances?