hat is pretty much what i have seen. the piston driven AR is sort of a answer in search of a question.
i had planned to put one on my 16" wilson 7.62x39 --but it runs so well i'm thinking why bother? the 5.45's also run well--
you know it MIGHT be worth it to do a pistol cal-piston driven AR --
the piston driven systems i have seen are so simple i have thought about building one myself (not out of a kit)--just for giggles--
they got these el-cheap-O gas blocks that are just about expendable for testing --