It occurs when the collar is not raised fully surrounding the planchet, and the metal is squeezed beyond the collar when it is struck. The technical term for this is a "Flanged Partial Collar Strike", but it got the nickname "Railroad Rim" even though it is actually the edge that is affected rather than the rim. Chris
It's suppose to go all the way around. The use of the word "Partial" is intended to mean that the collar was not fully raised into position. Chris
Chris' explanation is an excellent one. It is a partial collar strike. These errors are really cool with with coins struck by reeded collars.
