Jeff Makkos of Ohio reports finding a double struck 2007-P James Madison dollar in a Mint-issue set. The type of double strike involved is what errorists refer to as an “In-Collar Double Strike with Rotation Between Strikes.”

The cause may be due to two different scenarios.

The first possibility is that the coin was struck normally and then reentered the coining area falling back over the collar where it was forced back into the collar by a second strike in a position rotated just a few degrees away from the original strike.

Another possibility suggested by CONECA president Mike Diamond, is that coin remained in the collar while the inner sleeve of the collar broke loose and rotated within resulting in the same effect.

Because a coin normally expands in diameter ever so slightly upon ejection it is difficult for it to completely reenter the collar unless forced. The forcing of the coin into the collar often results in it only being forced part way and and edge that looks to have two levels or what is known as a “Partial Collar.” Makkos’ coin does not show a partial collar, indicating that it was either forced all the way back into the collar during the second strike or could have been in a rotating collar.
Read Full Numismaster Article by Ken Potter