The AR SUM is the new name for the old 300 RSAUM arbor for use with 223 boresight. The arbor has the same fitment; however, it does have a different name for and on the arbor.
Calibers it will fit:
300 RSAUM
7MM RSAUM
7MM RUM
300 RUM
(ARRSUM) AR 300RSAUM
$15.99Price