re: Official AR-15 thread

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A bit nitpicky, but the drawing is not accurate. Not to start the age old argument, but the bullet doesn't rise out of the barrel. The bullet vector should be dropping once it leaves the barrel. The line of sight vector should start at the rear sight and intersect the front sight, not start at the front site. This allows for a more true drawing where the rifle is angled up a tad and the bullet still interects the line of sight twice.

Yeah I noticed that as well. Probably could have picked a better image

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Quick question for anyone who can answer on red dots. When aiming at a target using the Lower 1/3 co-witness, am I aiming the red dot directly on where I want the bullet to impact OR do I aim the dot slightly above where I want the bullet to impact? I’ve watched numerous videos and they never clearly explain that part. TIA.

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The two are NOT dependent on each other. You sight them in completely independently. They don't even have to be sighted in at the same distance. For instance, if you wish, sight the irons in at 50 yards and the RDS in at 100. Or, vice-versa. Or sight them both in at 78.3 yards if you wish. They work alongside each other, not together. Also, RDS don't suffer nearly as much from parallax as iron sights. So, as you move your head relative to the sight axis, with iron sights you quickly lose your sight picture and can't hit your target. With the way RDS operate, if you can see your target and the dot is on your target, you will hit your target, regardless of the position of your head, the location of the dot in the reticle, etc. One of the things many RDS classes do is to black out a lot of the reticle glass with a Sharpie to force you to line up off-axis and trust that if you can see your dot on your target, you'll hit it.

The co-witness deal simply refers to how high above the axis of the barrel the RDS is. An RDS with 1/3 co-witness simply means that it is mounted higher so that when you are looking at the dot in the center of its reticle, the iron sights are below your line of vision. Some people prefer this. For instance, they may have fixed iron sights that they can't flip down and find it hard to ignore the irons when using the dot with an absolute co-witness.

An absolute co-witness means that the RDS is mounted lower, so when you look through the RDS and have the dot centered, the irons will be directly in your line of vision. If the two sighting systems are co-witnessed and sighted in for the same distance, then you should see the RDS right on your front post when you have a proper sight picture on your iron sights. If you have different zeroes, the iron sights will still be in the line of sight, but the front post of the iron sights will not be lined up exactly with the rear posts or the dot because of the different zeroes.

Basically, regardless of how you're set up, you put the dot on what you want to hit and ignore the iron sights. I use absolute co-witness and flip-up backup irons on my rifle, so I don't even see them when I'm using my optics. However, if I need the irons, I flip them up and my cheek weld is exactly the same as when I'm using my optics. With 1/3 co-witness, your cheek weld will likely need to be different between the two systems because their sight axes will be at different heights above the barrel axis.

Is the Smith &Wesson MP 15 Sport II a good one? Is $730 a good or terrible price? And it says it’s a 5.56 but under ammo it says .223, it can do both safely right?

Thanks!

It says in it’s description it’s chambered 5.56mm but under its specs it only lists.223 as its caliber