Part VI. Striking Errors:

Abnormally Strong Strikes:

Due to Elevated Ram Pressure:

Encircling pressure bumps

Definition: A circumferential arrangement of bumps that are pushed up along the design rim during the strike.

This 1974 quarter shows an encircling array of pressure bumps that are strongly developed on the reverse design rim and weakly expressed on the obverse design rim. The reverse bumps encompass approximately 220 arc degrees. The strongest of these pressure bumps occupy the entire width of the design rim. On the obverse, weak pressure bumps extend from 7:30 to 9:00.

Each pressure bump coincides with the location of a vertical reeding groove in the coin’s edge. The reeding on this coin is understandably very well struck.

It’s clear that pressure bumps are a manifestation of elevated striking pressure. But it’s not clear why we see bump development instead of a fin. In specimens where a strong fin is present, you do NOT see the development of pressure bumps along the internal face of the fin.

Pressure bumps are very rare while fins are relatively common. It’s not clear why this should be the case. Discovered by Keith Christenson.