The Grendel P30 and AMT AutoMag II have been on the market for several decades and, in many respects, could hardly be more different. What they share is an unusual chambering for a semi-automatic pistol: the .22 Winchester Magnum Rimfire. We took a close look at both pistols, which can still be found on the used market or, in the case of the Grendel, survive today in a substantially evolved …