1. I've said it before and I'll say it again. The Piston upper for the AR is the evolutionary path the AR platform will follow.
2. The concern over odd barrel harmonics is not something that is affecting at typical engagement ranges of both the 14.5" (MIL issue M4) or 16" weapon. What is the typical engagement range? Sub 200m, typically stated by the military as 50-150m.
Yes, the typical AR configured for long range engagement (SPR and DSM rifles w/ 18-20" barrels) there will be some degree of impact if a Piston was to be utilized. But that is not the case for the Military configured weapon. Gas blowback systems will be continued in that role so long as the AR platform is utilized.
3. POF and LWRC filled the gap that H&K so blatantly created when it refused to sell to the US civilian market. Shame on H&K, for that, I won't even consider buying a 416 or 417 upper.
Other companies have created replacement options (such as those listed throughout this thread) and some such as Robinson (XCR), MagPul (Masada) and a few others have completely moved away from the AR total form and have simply utilized the best portions of the AR and or utilized AR basic geometric standards (Mag well, trigger and grip/grip angle, ect..) Regardless, all of these systems are designed around a Piston system that will allow for the best of the AK and AR systems while incorporating the latest materials, metals and production sciences.
I'm personally leery of the the drop in piston systems because they seem extremely half baked and marketed towards those in the civilian market who just don't know any better.
The dedicated uppers are going to be far more stable (harmonics wise) because they have the additional design considerations incorporated.
The Piston system "solution" is little more than a way to extend the already sunsetting life cycle of the AR platform. It's old, still fairly effective, but there are several systems coming into maturity that finally exceed the capability and functionality of the AR. The Military is obviously taken this to heart, hence the SCAR and XM-8 programs. Coupled with the wide acceptance of the G36 series by European military and security entities, yet another blow has been made to Gas Operated systems in the grander scheme.
I love my AR's, always will. It is the weapon that saved my life when I needed it and I will always have several. But I am a realist as well. The AR is in the twilight of it's useful role in the world of small arms. Much as the AK-47, the AR will become and typical 3rd world Military and Police weapon, while 1st world Militaries and Security organizations will adopt more modern constructions like the G36, SCAR, Travor (SP) and what ever that new Chinese bullpup is called.
Point being, sure, the Piston upper is a pretty solid design, but it is most likely the last major evolution in a very long and relatively stagnate design and use cycle of the AR platform.
