The 1873 Open 3, No Arrows Half Dollar is the replacement for the Closed 3 version, issued earlier in the year and found to be defective because the Closed 3 looked so much like an 8.
According to official records, the mintage of the Closed 3 is slightly more than 2.5 times that of the Open 3, but catalog valuations indicate a much different picture of the relative rarity. Depending on the grade, an Open 3 can be worth anywhere from 40 to almost 70 times as much as a Closed 3 (this relationship only applies to the No Arrows versions and has nothing to do with the With Arrows, Open 3 variety).
Any 1873 Open 3, No Arrows Half Dollar above Extremely Fine is a real prize. Only a very few Mint State examples are known, and even those are low end. If an MS64 example came on the market today, it would create a considerable stir since it would be the finest known.