Hello, I just recently got my S&W M&P 15 and I am hoping to co-witness the sights, but I need some help. So I plan on getting a Sightmark Ultra Shot Plus Red dot sight and I want to co-witness it with the iron sights that come on the S&W M&P 15. As you all know, the M&P 15 comes with an A2 fixed front sight. So how can I co-exist the sights without the front sight interfering with my red dot? Please help.

Just mount it. Turn it on, and the dot will either be touching the top of the front sight post or slightly above it. As to where to mount it, that's user preference.

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Ok, where do you suggest I mount it? This is my first AR-15 so I don't necessarily have a preference. What do you think would be best?

First, let's make sure you understand what co-witness means... you are going to see the front sight in your sight picture... how much you see is determined by how you mount the optic, either absolute co-witness or lower 1/3. Where you mount the optic is up to you... I prefer for a red dot to be mounted as far forward on the receiver rail as I can get it.

Ok, thanks. Do you mind if I ask why you like the red dot as far up as possible?

I have tube style red dots. With it mounted further back, it limits my peripheral vision around the optic.

I did 1/3 co-witness and it works great.

Ok great! Thank you guys for all the help!

I just looked on their web page and in their Q&A section, they state that it is lower 1/3 out of the box. They also said you would need a riser to get to absolute co-witness, which I don't understand... if you wanted absolute, you would need to lower the sight, not raise it, and it doesn't appear that you can lower this particular sight because of the housing.

I always do absolute.. keeps everything consistent. I like to use iron sights in the day light, but if shooting in low light, i know the red dot is lined up to the iron sights.

That sounds good because I want to do lower 1/3 anyways. If I do absolute co-witness, wouldn't the iron sights block my red dot since my front sight is a2 and doesn't flip down. If I do absolute co-witness with a fixed a2 sight, it's basically like using iron sights all the time right?

No, not at all. When shooting with a RDS, you keep both eyes open and focus on the target down range. The dot will appear to float on the target. I don't even notice the front sight.

Oh ok, gotcha. Thanks for the help!