Originally Posted By nukeman:
I have a degree in Metallurgical Engineering..but the reason I think the pistol frame dosen't see much stress is because it's pretty much just holding those metal rails which the slide sits. On a AR lower, you have a stock attached to the back, a pistol grip, and 2 points where the upper is attached. If you are shooting from a prone position (for example) with a sling, then you have several bending, torqueing, and tensile forces happening on the reciever at the same time. That's why I see it as a different issue. Maybe if you held your AR with 1 hand like a pistol, then polymer might be ok.
That's just my opinion, for what it's worth.
Also think about where the forces of recoil enter a pistol frame vs an AR lower. The impact on a pistol is in the front of the frame and is dissipated through the entire frame in compression. The impact on an AR holding it loosely against a shoulder or as a pistol it all concentrated on the buffer tube tower (in tension) when the buffer/bolt carrier reach the end of stroke...