That there, is a picture of the QRBP with a W209 primer in place. Note the rim. The top of the W209 is below the rim. The 1.644" measurement is the length of the QRBP. The 1.644" measurement has naught to do with the W209. Every primer from the STS to the W209, when in the primer pocket will measure 1.644". The caliper doesn't touch the primer.