Ron Guth:
With a mintage of nearly 900,000 coins, the 1840-O Half Dollar is a relatively common coin. The survival rate of this date is higher than most of the other O-Mint dates from the 1840s, though it is not as high as the 1845-O or the 1846-O. Mint State examples are somewhat scarce, but can be found frequently in grades up to MS63. No Gems exist, though a few MS64s come close.
The strike on the 1840-O Half Dollar is above-average for a New Orleans product. Mintmark sizes and positions vary. One variety has a rather obvious die break that splits the lower reverse nearly in two.