Originally Posted by Kokanee
You're aware the M16/C7/Armalite etc system is a closed bolt system right?
I think he's referring to the misnomered "open bolt" (should probably be "open chamber") version since he was asking for a gas blowback.
And given that, there are currently no out-of-the-box gas C7/C8s, so you need to build your own. As such, I would make sure whatever platform you select is as compatible as possible with RS and commonly available airsoft accessories.