22 caliber Marlin rifles were the first Marlins to be Micro-grooved, with the first Model 336 to feature Micro Groove rifling being the 1955 model 336SC chambered in 219 Zipper. As noted the change to all Micro Groove rifling in center fire rifles took place in early 1956; so it is not uncommon to find the occasional 1956 model 336 with the old style Ballard rifling.