Seem to of lost the set screw for my rear sight on my .22 m&p google failed to find a replacement, will one from something else work or is it time to upgrade the factory sights?

I can't answer you directly but I can remark to the fact that my sight blade popped off the first time I shot the gun. Made sure to loctite that puppy in when I got home. I'm surprised it doesn't come with some threadlocker from the factory!

Here's a few things Google popped up - someone says the M&P9 and M&P22 use the same set screw: 5/40 x 3/16". McMaster has flats in 5/32" and 1/8" lengths.

http://www.glocktalk.com/threads/s-w-m-p-rear-sight-set-screw-size-and-link.1467908/

http://smith-wessonforum.com/smith-wesson-m-p-pistols/269655-set-screw-size-m-p9mm-rear-sights.html

Thanks had emailed S&W about buying one but havent heard back from them, will loctite the new one. I never touched the original have probably 1000 rounds through the pistol so far when it was lost. Great gun but I guess the only thing they torque down good at the factory is the thread protector.

Gotcha! My sight blade popped out in the first 50 rounds which clued me in on the issue and I was able to save the screw. Regarding the barrel wrench, the replacement version from EWK is pretty awesome. I also bought a non-threaded thread protector for easy field stripping when I don't have a suppressor (which is always right now). The aftermarket/community is growing for these finally!

Good luck

Mine did the same thing. I sent it back to S&W and they cemented that sucker in there. Now it shoots about 3" left and I can't adjust it.

I'm going to swap them for some aftermarket sights.