bkt - I don't have any evidence to support my position to be flat out honest.
We ordered one of the bolt action style uppers into the shop about 2 years ago. We fitted it to a stock A2 lower, with the fixed plastic stock and we sat it on the counter.
At the same time we had a 33" long 1.5" diameter bull barrel benchrest .50BMG that was in for some fine tuning before B.R. Season sitting on a wood stock with a 4" wide tracking base that probably weighed in the 50# category.
I looked at those two guns and just sat there for a minute thinking it through in my mind's eye.
When that big bastard round gets touched off on the benchrest gun, the whole thing is going to slide backwards on the tracking sled to help ease the recoil. The action was this monster hex design and it was mated up to the wood stock with some serious action screws, along with the back of the receiver being deep inside the "meat" of that wood stock.
And then we had a 30-something inch, monster steel upper with this big friggin tank style break on it mounted to an aluminum AR lower by two pins and that big assed action was sitting behind some plastic in the form of a stock.
Now, what a lot folks don't know, or don't think about, is that there are several factors that happen when a round goes off.
First is the initial back pressure from the explosion of the gunpowder. Everyone expects that.
But almost immediately after that, there is a SERIOUS amount of torque that is applied in the form of that bullet being propelled at force into a set of lands and grooves that cause it to start rifling.
That is the same type of torque as when you are drilling something and as you get to the end of the cut and the drill bit binds up and the drill wants to jump out of your hand and take your arm with it.
That is not lateral, front to back, pressure or force. That is a twisting, turning, wanting to spin that upper receiver like a top, sort of pressure.
And that pressure is being countered by a couple of pins that go through a piece of aluminum.
Now, I am sure people a lot smarter than me probably graduated from MIT and looked at all these forces and compared specs and weights and measures and potential until the cows came home.
But I personally just don't think that is a recipe that I would want to trust.
Your Mileage WILL vary I am sure. This is just one lowly shop rats opinion.