I purchased a 15-22 with a factory installed MP-100 optic at Cabela's for $349. I took it to the range and had a lot of fun with it. One of the guys working at the range recommended that I remove the optic and tighten up the mounts because they frequently aren't installed correctly by the manufacturer. I didn't have a wrench with me so I just went for it and sighted it in at 25 yds (max at this range). Half way through the process, the POI shifted down by about 4 inches. Apparently, he was right. I dialed it in and it held after that. I will be tightening the mount before my next visit to the range.
I plan to put iron sights on this rifle. The manual says that the height of the optic is 3.25 in. The center of the front lens is 1.5 in. above the rail. I would like to lower 3rd co-witness with the iron sights. Will this work with this mount or will I have to get a taller mount? Does anyone have a recommendation for relatively inexpensive dual aperature iron sights?

The 4 MOA dot it a bit large for precision shooting, even at the lowest brightness. The green dot is much brighter and larger than the red dot at minimum brightness. That is not the case with my Vortex Strikefire II optic on my Ruger AR556. Is this dot size difference typical for this low end optic or is there something wrong with mine?

Can't go wrong with a set of Magpul MBUS sights. They ship with most 15-22's and are relatively inexpensive, especially when on sale.

As far as the difference with dot size, you answered you own question, the MP-100 is a low end optic.

Congrats on the new gun. Regarding co-witness and if you go the MBUS route, here's a bit of info:

SPECIFICATIONS

MBUS – Rear

Weight, w/ hardware: 1.3 oz.
Height above rail, stowed: ~0.51 in.
Center of aperture to top of rail: 1.42 in.
Length, stowed: 2.6 in.
Length, deployed: 1.5 in.

Therefore, just get the same measurement (above top of rail to center of glass) and go from there.
MBUS(R) Sight – Rear

Believe sights on M4s, etc are 2.6" above bore or within 0.1" of that.

Looking at an online pic, it looks like it's mounted at 1/3 co-witness. Give S&W a call. They should know.

S&W has agreed to replace the optic. They did not send a return label so I guess I will have to pay shipping. Hopefully the new optic will be better.

Also, they confirmed that my rifle is not affected by the safety alert. It was manufactured on 6/7/2019.

1. If you tightened it and all is well, why swap it?
2. If S&W determined there was an issue with it on their end, call them back and ask for a return label.

Update:
I looked at my Vortex Strikefire II optic and I am seeing a bit of distortion in it as well. It isn't nearly as bad and the MP-100, but it is definitely there. Apparently, my eyes have changed in the last 2-3 months. I went to the optometrist and ordered some dedicated shooting/safety glasses. I have the beginnings of cataracts and he thought that it may be getting worse. Getting old sucks! I have been using progressive lenses for years. He thinks that I will do better with bifocals, so that I will be looking through a fixed, wider area, instead of the narrow area seen with the progressives.
I went back to Cabela's and looked at the MP-100 optic that they had on the display model. The distortion was the same as mine, so a replacement isn't going to solve anything.
I saw a couple of videos recommending Holosun optics for people with astigmatism. I looked at a couple of different models at Sportsman's Warehouse and they looked MUCH better. I think it may have more to do with a smaller dot - 2 MOA on the Holosuns vs 4 MOA for the MP-100 and my Vortex optics. I may buy one of the Holsun or similar optics, if the shooting glasses don't make a significant improvement.

I don't know if this would be something that you might consider, but, why not get the best of both worlds and get something lime a 1x-4x, or, 1x-6x scope with an illuminated reticle? At 1x you can easily speed shoot multiple targets, and still zoom in for distance targets. I put a Tru Glo OMNIA 4 (1x-4x) on my 15-22 (on a Antibal QD mount) and it's a great scope for the money. For just under $200.00 you get the scope, mount (non QD), flip-up lens covers and a throw lever. Target turrets, Red illuminated no frills reticle, multiple brightness intensity levels, and defaults to black if not turned on, or, if battery dies. It doesn't 'fish-eye' at 1x and has real clear glass. It's a great scope for the money!

After doing a bit more research, I decided to look at some other optics with a 2 MOA dot. One video about astigmatism recommended one of the Holosun optics, so I took a look at the Holusun HS503R circle dot sight. The dot is much sharper than the MP-100 and my Vortex Strikefire II. The circle is very sharp and helps in target acquisition. There is a very small amount of distortion in the dot, but it is negligible. Sportsman's Warehouse had 10% off for loyalty members on Sunday so I bought it. I mounted it and took it to the range and sighted it in. I am very happy with it! I am hoping that the new glasses will improve the image for the Vortex sight. It is not a big deal, as I can still shoot very accurately with it. I believe that the smaller dot size is the fix for me.

Glad you have reached an acceptable resolution. I have a couple of Holosun optics and really like them. One is tube-type and the other is reflex.

As you have discovered, an actual "red dot" optic does not play well with astigmatisms and/or other eye abnormalities.

In most cases you have the option of a variable scope, fixed scope, prism scope. I have a few prism scopes in 1x, 2.5x, 3x and really like them, especially the etched reticle. I rarely use the illuminated reticle but it's there if needed.

Fortunately for you, the Holosun 2moa dot came through for you. For some folks, even a 1moa doesn't work. It really depends on the individual and any given optic (red dot). With some folks using hard sights along with a red dot, peering through the small peep aperture will "scrub" away much of the roughness surrounding the dot.

Happy shooting.

I spoke with S&W this morning and they have agreed to replace the optic with a magazine for my 380 EZ. That works better for me, since I was going to have to try to sell the optic or just eat it. I am happy with the resolution.