I installed a set of Ameriglo Defoors a few months ago on my 43X and liked them so much I installed a set on my G17.5. Yesterday, I was practicing with the Slimline and was getting nice tight groups that were consistently at 9 o'clock of my aiming point. My presses felt clean but no matter how slowly or quickly I shot, the group was always a few inches to the left of the X-ring. I chalked it up to a bad grip and figured I'd work on that when I got home.
After I cleaned the gun and wiped it down, I noticed that the rear sight had drifted all the way left in its dovetail. I tried pushing on it but the sight wouldn't budge. I went back to the range the following morning to borrow a hammer and punch. It took some forceful taps to sort things out and after a few magazines, I was able to re-establish a zero. I then applied silver Sharpie witness marks to the left and right portions of the dovetail. If the sight moves, I should see some sliver of black and correct things before they get worse.
I know Ameriglo have fans here, as well as contracts with Fed/.gov agencies like the FBI. I've never experienced this drifting before so forgive me if I'm wondering if such is typical of rear sights that do not have set screws.
Is this drifting to be expected? Any tips to mitigate this movement?