I recently picked up a Marlin 81DL which was determined to be C&R eligible by certain features. It does not have a grooved receiver which has me wondering if this can be used to date .22's? Does anyone know when they started offering grooved receivers? The Mossberg 146a was made 1954 to 1958; my example has a grooved receiver. Does anyone have a .22 with grooved receiver known to be older than that?