^^^^^
AGREE, wholeheartedly!!!! There is absolutely no need to grind on ANY magazine follower button. While the follower button diameter is certainly smaller on the early magazines (.250 diameter) than the follower button diameter on the Ruger Mark II magazines (.326 diameter), the larger follower button will indeed still work. What Ruger did do when the Ruger Mark II's came out, was increase the size of the radius in the grip frame for the follower button from 7/16-inch to 1/2-inch, but still, the larger size follower buttons do work in the older grip frames. I've tried them, do it yourself to see that they work.
When the Ruger Mark II was introduced in 1982, there were a couple of changes made to improve the Mark II, over the Mark I, or early Standard. One main improvement is the addition of the bolt stop assembly parts. Another change involved the "scallop-cuts", just in front of the bolt ears on the receiver. That was done to get a better purchase on the bolt ears for cocking the pistol. Those parts in the Mark II are activated by the magazine follower button. The A100 grip frames had the magazine follower button clearance radius, stamped into the grip frame, moved from the right side of the grip frame over to the left side, same as the Mark II grip frame. Previously, on the Ruger Mark I pistols, there was no hold-open mechanism in place to hold the bolt back after the ninth round was fired and the magazine emptied. The safety on the Ruger Mark I pistols was used as a 'manual' bolt hold open device, when the safety is pushed up and the front end of the safety is hooked into the left side notch in the bolt. Now, to get things even more convoluted
, magazines for the (catalog numbered A54) early grip frames can only be used in the A54 grip frames because there is no slot for the magazine follower button on the left side of the magazine, only the right side. Magazines that were made to accommodate the A100 grip frames, and all Ruger Mark magazines thereafter, have magazine follower button slots on both sides of the magazine and will work, in even the early pistols, except for the 22/45 style base plate type, if the follower button is moved to the right side of the magazine body, even the Ruger Mark III bodies. I've tried 'em. Then, you can have a magazine that holds 10-rounds.
#1. Ruger Mark I & Standard for the A54 style grip frame.
#2. Ruger Mark I & Standard for the A100 style grip frame. Notice slots on both sides. These magazines will also work on the A54 style grip frames.
#3. New style Ruger Mark I & Standard "replacement" magazines for the above. Still hold 9-rounds
#4. Ruger Mark II style magazines. Introduced in 1982. Hold 10-rounds
