M&P 9 Sight Problem

rthom08

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First off, this may run a little long, so I apologize in advance. Note that all of my shooting is done at around 10 yards, and I have been using 147gr American Eagle ammo for the most part.

About a month ago, I purchased a full size M&P 9mm from my LGS and had them install some Trijicon HD night sights. I have put 800 rounds through it so far with no FTF, FTE, etc., but I noticed it consistently shot to the left. At first, I attributed this to user error since I was still getting used to the pistol, but it seemed to progressively get worse, ending up around 3-4 inches left of center.

Fast forward to a couple of days ago at the range. At this point, I began to think that it was the gun and not me. When I looked closely, I could see the rear sight had slid almost all the way over to the left side of the slide, so I loosened the set screw, drifted the sight back to center, and retightened the set screw. Once I got the sight positioned where I wanted it, I ended up drilling out the center of the target with the few remaining mags of ammo I had.

Fast forward again to today. I go back to the range, and everything started out fine. Several mags in and I notice my shots starting to drift to the left. I looked at the sights and notice that they had slid back over to the left of the slide yet again. The set screw was still tight, so I'm sure that wasn't the problem. When I loosened the set screw, I noticed I was able to manipulate the sight back and forth a little bit with just my fingers. Same as before, get the sight centered, and my shots are hitting dead center.

Anyone know what might cause this? Does it sound like the gunsmith maybe went the wrong direction when removing the stock sights and boogered up the dovetail when installing the night sights? Also, if this is the case, what course of action would you recommend? Thanks in advance for any and all replies.
 
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I had a similar problem when I installed my Big Dot Sights on my FS 9. After about 10 or 12 shoots down range, my rear sight would loosen up. I had the gunsmith at the club look at it. He said that a little loctite and some filling down to get the rear sight flush would take care of it. Have not had a problem after doing the fix.
 
I had a similar problem when I installed my Big Dot Sights on my FS 9. After about 10 or 12 shoots down range, my rear sight would loosen up. I had the gunsmith at the club look at it. He said that a little loctite and some filling down to get the rear sight flush would take care of it. Have not had a problem after doing the fix.

When you say your sight loosened up, are you talking about the set screw loosening and backing out? If you are, then it seems like my issue is a little different. My set screw is still very tight when I inspect the sights after I notice them moving.
 
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Yes, because there was a small gap and the set screw could not get all the way down. That was the reason for the filling. And because it is my EDC I don't need to adjust the rear sight, so that was the reason for the loctite.
 
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