Originally Posted by Snakedriver
The 5-teen Remington's in the late 50's and into the mid-60's had a "X" after the model number to denote a factory grooved receiver. For example, 511X .
Some of these fine old rifles have also received the the scope grooving after leaving the factory from some gunsmiths who have the equipment to do so. Those rifles will obviously not have the "X" after the model number.
Thanks interesting to know, I will have to go home and take another look at my rifle.