Apparently quite a few people have lost sight of the fact that the AR15 was designed with an "in line" stock.

And that due to its 2.5 inch deviation in sightline-to-boreline, most of the butt stock should extend above the plane of the shoulder(s) in order to achieve a proper (and comfortable) cheekweld.

It makes no never-mind to me what "new" techniques people devise to accommodate the shooting discipline in which they participate but the effect it has can obviously be confusing to the novice shooter when considering such techniques and associated "hardware requirements".

Maybe I should create a website to document the AR15's design principles and idiosyncrasies lest they be lost forever to future generations of shooters.

Be my guest.

The part of your reply I highlighted is exactly what the girl in the video is doing but then she has a riser on the butt stock (to compensate?). It's like the math (engineering) of the AR15 "in line" butt stock has all but been forgotten.

Sigh.

Do you mean lever arm as it relates to torque physics?

And that with only the bottom 1/3 of the butt stock making contact with the shoulder that it creates a "lever" at the point of the firing hand on the grip?

And that this arrangement causes rotational force (torque) that is detrimental?

If I'm understanding you correctly, then no, the natural sightline/boreline of the AR15 with its in line stock creates perfect alignment with the eye and any given sighting system that is the standard 2.5 inches above the boreline and 1/3 shoulder contact.

I've demonstrated the same thing as Miss Yackley (at about the 40sec mark of the video) to students re: gripping the rifle with only the firing hand and pulling the rifle into the shoulder with only the bottom 1/3 of the butt stock making contact with the shoulder and never experienced any undue rotational tendency.

The AR15 in its basic form factor (A1 / A2 / M4) is a well-balanced weapon. While I have fired AR15's with low power variable optics, it's always been on one of the aforementioned configurations.

Not knowing the make up of the rifle in the video, perhaps the AR15 is a totally different animal with longer, lightweight (carbon fiber?) or heavy match barrels.

Don't get me wrong, specialized configurations can and do require specific techniques on occasion and I kind of alluded to that in my first reply. But I also tried to point out what I thought was a fair criticism in that the entire butt stock is making contact with her shoulder and yet she has attached a riser to the butt stock. Just seems like a bit of a contradiction.

I do agree with her about stance.

IIRC, an aimpoint's 30mm tube requires a mount that puts the C/L of the optic at a little over .80 inch above the receiver in order to achieve an absolute cowitness with the iron sights (please correct me if I'm wrong).

So even if one is using a high power variable with a large (50mm) objective lens (and a folding front sight), 50mm - 30mm (aimpoint) = 20mm / 2 = 10mm, a mount or riser affording another 10mm or .39 inch for the obj lens to clear the receiver. Even then, .80 + .39 = 1.19 inch.

The lower 1/3 cowitness needs about 1.00 inch so with 1.19 I can understand the possible need for a riser on the butt stock lest one begins to have to rubberneck to get their eye behind the ocular lens. In my mind, if my math is correct, I can't figure the need for a mount/ring providing more than 1.25 inch (for a 50mm scope) and certainly not a 1.93 mount/ring?

This is certainly an interesting topic.