A partial collar is sometimes called a railroad rim when a reeded edge coin is involved as the line resembles a rail and the reeds resemble railroad ties. Partial collar coins strikes occur when there is a malfunction of the striking press.
A partial collar error is when the blank or planchet does not fit INTO the striking collar, but instead is mis-fed, and the blank or planchet is seated on TOP of the collar, (not IN it), so that when the dies strike, the pressure pushes the B or P a bit into the reeded edge collar - thereby a 'partial collar', aka: railroad rim. Many Type 1 Blanks get struck like this, because they are slightly larger than the Type 2 Planchet, and so do not fit into the collar. Hope this helps a bit.....
