While the subject and study of abnormal reeding has been around for two or more decades, this sub category focuses on a coin of recent vintage, a 2008-P New Mexico state quarter. First, however, a brief history of reeding variants.

One of the best known examples is the “infrequently reeded” 1921 Morgan dollar. A rather extensive discussion of this variant can be found on pages 113-144 of Frank Spadone’s “Major Variety and Oddity Guide to United States Coins” (8th edition). Spadone notes that there are only 154 reeds versus the normal 188 reeds found on other silver dollars produced in 1921. He further observes that the grooves between the reeds are simple slots rather than the more elaborately defined notches seen in other dollars. He suggests it represents a first attempt at fabricating a collar for a denomination that hadn’t been minted for 17 years.

A very uncommon cause of abnormal reeding is collar damage or improper machining. Both Arnold Margolis and Alan Herbert report the use of a broach to create the ridged working face of the collar. A broach is a cylindrical tool with longitudinal ridges that is hammered or driven into a smooth, unfinished collar to create the ridged working face. A worn or damaged broach, or the improper penetration of broach, can theoretically produce abnormal reeding. It’s quite possible that other techniques are periodically used to create the ridged working face. It would be a simple matter to cut evenly-spaced grooves into the working face with a machine tool.

This rather roundabout introduction leads us to the focus of our entry – a 2008-P New Mexico quarter with abnormal reeding. The reeding on this quarter takes the form of low, thin ridges separated by broad, flat valleys. A normal quarter shows taller, wider ridges separated by deeper, V-shaped valleys. The ridges on the working face of the collar were ground off almost to their bases.

An essentially identical error is known on a 1964-D quarter.

Below is a 2008-P New Mexico quarter. The left image displays normal reeding. The right image displays abnormal reeding. Center image is a comparison edge view of both the normal and abnormal reeding.

http://www.coinworld.com/articles/a-second-case-of-abnormal-reeding-on-a-state