I'd like to say this proved my sights were off, but it actually proved they were dead on (Smith and Wesson M&P9 2.0). Oh well, I guess I have to learn how to shoot better. This boresight was super-simple to use aside from handling the tiny button batteries and end cap. Fits nicely in the bore and allows the slide to close. One tap and the boresight comes out. The laser pip is very bright (red) and easy to see. Great product
Update: I check mine by putting the gun in a woodworking vice. the pip hit the same spot if I took it out an rotated it. Most sights only adjust for windage so you can only adjust side to side, not up and down. If you are adjusting a laser sight, just line it up with gun sights initially and tweak it at the gun range.

I wasn't able to locate a 9-mm laser boresight that doesn't have reviews stating that the device jams in the chamber. This item had better reviews than most so I took a chance. This one jammed in my Glock 43, Glock 19, and 9-mm AR pistol despite the fact that I gently rode the slide forward. The instructions state that "in some pistols it is not necessary to have the chamber closed for it to work properly," but it does not identify those pistols. The instructions also advises that you "avoid strong bumps, blows or impacts to the device." Pounding the back of the slide against my hand wasn't enough to dislodge it. I had to give it a firm tap on the gun pad on my workbench to dislodge the device in all 3 weapons. If you have to dislodge it, I suggest you put something soft behind the device, leaving just enough room for it to dislodge and yet prevent it from falling and bouncing around which could possibly knock the laser out of alignment.

I love the idea but there does not seem t be any QA for this product. I received two sets and neither laser was aligned corrrectly. Unless the laser is aligned perfectly within its housing, the laser will not point straight. In my photos you can see how you must check your laser before a) using it to zero your weapon and b) before giving a review or getting rid of the packaging.

1) Remove the barrel from the weapon and clamp it to a flat surface (I used a metal table leg.)

2) Mark part of the back of the laser and consider that part "up" for now.

3) Insert the boresight into the barrel wth the mark in the up position

4) 5+ yards away mark with tape and a dot of ink where the laser hits a wall (this will be the reference point)

5) return to the laser and carefully rotate the boresight (or remove and reinsert) so that the mark you made in step 2 is in the opposite position (down if it was up).

6) walk back to the wall with the tape and see f the laser dot matches up woth the existing mark.

7) Repeat steps 3-6 as many times as you want to validate the result. As long as the dot is in the same position when the mark on the back of the boresight is in a specific position you will know that the barrel has not moved during the process of you removing or spinning the boresight.

The point to all of this is that for the boresight (any boresight) to work properly the red dot on the wall should always be in the same exact position no matter how the boresight is rotated in the chamber/barrel. If the red dot does move (in my case it moved about an inch for both boresights) it means any "zero" you were to get by using this thing will be off.. and not even close.

If you don't check your boresight like this and you are still getting OK groups after zeroing your sights there is a good chance that you are not shooting consistently or that you are cheating yourself out of even tighter groups.

This test only takes a few minutes and is a great way to ensure your boresight actually works properly. Unfortunately for me, after two separate shipments, each product failed the test. :(

Also, if there was some way to adjust the alignment of the laser and it's housing I am confident that using my testing method we would be able to align the laser and have a great boresight. Unfortunately, it didn't seem like the tiny screws actually did anything but maybe hold the laser inside of the housing

I bought this to zero in a couple of red dot sights I have , one on an M&P 9L and one on a G34.
I have them zerod pretty good already , wanted to see what the laser says.
In both guns the laser is about about 2 inches high where the red dots currently showed, which
caused both guns to shoot low almost off paper at 50 feet.
It's nice and bright , but way off. had to use a bore cleaning rod to get it out of both guns as well.
Very disappointed with this thing.

Be sure to clean thoroughly with some rubbing alcohol before using. Mine came with a wrapped sticker that left significant residue. I could totally see this causing chamber jamming as well as alignment / accuracy issues. Manufacturing tolerances of weapons will lead to varying levels of success with this tool. When I roll the boresight across a flat surface I see no elevation variance in the dot at all at 60 ft so it's well made. Repeated chambering in my Walther PPQ however saw +/- an inch or so of variance at 25 feet compared to a laser sight, both horizontal and vertical.