1840 Broad Mill

The 1840 broad-mill half eagle is a transitional holdover. Philadelphia entered the year still using the 22.5 mm planchet stock and collar diameter that had defined the 1839 issue, then switched to a 21.6 mm format partway through production. Coins struck on the older wider format before the changeover are catalogued separately as the broad-mill variety. The 137,382-piece Philadelphia mintage reported for 1840 covers both formats; the broad-mill share is the smaller early portion, struck during the first stretch of the year before the new dies and collar took over. By August the Mint had committed to the narrower 21.6 mm standard that would run through 1908.

Attribution is dimensional. The defining check is diameter, which should measure 22.5 mm rather than the standard 21.6 mm used after the transition. Calipers settle the question on any unattributed example, and the difference is visible to the eye once a known narrow-mill 1840 sits beside it: the broad-mill coin shows a wider rim on both faces. Edge reeding runs finer than on the post-transition strikes, another tell that survives even on worn pieces. Weight stays at the standard 8.359 grams since the planchet mass was unchanged, and specific gravity should sit near 17.16 for the 0.900 fine alloy. A coin that reads 21.6 mm belongs to the standard 1840 entry, not this one.

For collectors, the broad-mill 1840 sits in the variety specialist lane rather than the type lane. Most date sets are filled with a standard narrow-mill example, and the broad-mill coin is pursued as a separate target by collectors building out the early-Liberty subtypes. Survivors are scarce in all grades and rare above XF, with Mint State examples appearing infrequently enough that auction records track individual reappearances. Pricing carries a meaningful premium over the standard 1840 once attribution is confirmed, and unattributed examples in dealer inventory occasionally turn up at standard-date money. Anyone working the early years of the series benefits from carrying calipers. For wider context, see the Liberty Head Half Eagle series history.