Your problem intrigues me. I have examined many makes of the Ruger 9 & 10 round magazines and their overall body length is identical. I have a Mark I and it can hold either capacity magazine. Perhaps you can examine your pistol from the bottom (magazine well) and ensure the magazine follower button is on the correct side for the scallop cut in your frame. The date of your pistol tells me the button channel of your pistol will be on the left (looking at your pistol from the bottom and with the barrel facing away from you). If this is the case then does your magazines have button grooves cut into both sides of the magazine body? If they do then you can switch sides of the follower button's location and you should be OK.