IMHO if you want a piston gun get one that was designed that way.
HK416,thats why SOCOM are outfitting SOPMOD M4s with them....cause pistons suck. I think the XM8 is awesome if a bit "starship troopers" looking.
I also love the XCR i think it has massive potential and still has the modularity thats great about the AR platform. the SCAR and ACR got screwed being so expensive.....still not clear on how a rifle that is mostly polymer is so damned pricey.
I'd be surprised it it was. What kills me is that so many people act like H&K invented the idea of a piston upper.
. . . . I thought that was Al Gore.
H&K actually is kind of the gun world's Al Gore, now that you mention it.