Normally there is a friction fit between a sight and it's dovetail,
but on my new M&P 9C the rear sight is so loose in the dovetail
that the sight slides freely in and out of the dovetail from either
direction. The set screw is only thing holding the rear sight in
the dove tail slot. If not for the set screw the sight would simply
fall out. I'm debating sending it back to S&W, but I suspect they
wouldprobably peen the top of the dovetail down a bit to solve the
problem and if that's the case I could do that and not be left
without the use of the gun for the time it would be back at S&W.

Any thoughts or suggestions?

If the screw holds it firmly then I wouldn't worry about it. It will make it easier to change the rear sight if you decide to upgrade it. I wish they were all like yours!!

You've got a valid point, it does make adjusting infinitely easier, on the other hand I'm hesitant to rely on the set screw alone. Always nice to have a little backup. I could put a touch of locktite on the it (not the allen screw) but
that isn't real appealing. I don't want the sight too snug either. I think I'll carefully (gently) influence the top of the rear portion of the dovetail just a bit, at least to the point that the sight won't fall out if the locking screw
backs out.

Thanks for the heads up.

Put blue Loctite on the threads of the set screw. That will hold it but you'll still be able to loosen it when needed. I had Wayne Novak put his sights on a Browning HiPower that I had. He machined it so that the sight was loose in the dovetail and held tight by the set screw. Since he is the master of how his sights are supposed to fit then I assume that loose is the proper way.

That's exactly how my M&P45 is, when I did some trigger work and removed the rear sight, slid out very nicely. Did my work snugged down the screw and haven't had a problem.. No need to send back to Smith, nothing wrong with it.

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Jack C

Remove the sight, take a punch and raise a couple of small divots in the flat of the dovetail. The sight will go back in snug, and it won't show.

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Pisgah

Thanks for the helpful comments. As an aside, this M&P9C is one
sweet shooting gun. With the APEX DCAEK kit and some polishing up the Trigger pull is at a crisp 4.8# and function is flawless.

A happy camper!

The Apex kit for sure is the cats meow.

I had the opposite problem with my rear sight. The set screw was so tight the allen wrench spun in the screw. Fortunately I had a small easy out set. Even with the easy out I felt the easy out was just about to lose bite when the screw finally moved. My sight itself was snug actually it wouldn't take much as a set screw to keep it from moving. I'm sure someone at S&W was snickering about the day some sucker was going to have to loosen that screw. LOL

The Apex kit made a 100% difference in the trigger both smoothness and trigger pull. Trigger pull itself dropped over 2 pounds. It would be so easy for S&W to do the same.

Pisgah has the idea here. Take a punch raise a couple dimples which should make the sight just a little snug.

Dan