When a metal loading nozzle breaks, its due to the material being too rigid and allows a 'wave of stress' to move across the material every time the gun is fired, right? What I'm trying to get at is resonance. Of course, I doubt that the metal loading nozzles will break DUE to resonance but the repeated cycle of the stress waves travelling through the (pot) metal nozzle will surely lead to a faster failure point than a plastic / POM one?
Some post all the way back in this thread about the Shooter's Design nozzle had a speculation that because the POM material bends; it is more durable. Hence, I would conclude that given the material can easily deform (comparing with metal and the stock plastic nozzle) the wave of stress can't develop as much as the metal nozzles since the shape of the nozzle (in microscopic scale) changes to prevent the wave from travelling too far within the material itself as well as the energy imparted on the nozzle will be redistributed to change the shape of the nozzle, thus reducing the overall stress developing throughout the structure.
I don't remember the key terms and theories from physics no more (studying civil engineering...it really is applied science..in the sense that you only apply it. I hate HK education) but I think I got the gist of it correct. If I'm wrong, feel free to correct me