I got a chuckle out of Mike Diamond's response to your coin: "Yes, a generic capped die strike in combination with a partial collar error".
I should have picked up on the partial collar but I was fixated upon the main error. That's why experts like Mike are great!
I very much respect Mike's knowledge and expertise in the error field of coin collecting. There is none better these days, including Richard Cooper ('coop") on this forum http://www.coincommunity.com/forum/forum.asp?FORUM_ID=5 .
I hope you continue your interest in this type of error. Back in the day I bought them at auction for between $3 and $15 apiece, depending upon the stage and whether it could be identified as a brockage of counter-brockage.
Jim
(continued)