When you’re quieting down a semi-automatic firearm, most of the residual sound is going to come from the action itself. You’ve got a hunk of metal sliding back and forth, banging against other metal bits and venting gasses — you bet it’s going to be heard. The solution used to be to turn the gas system off at the gas block, but Innovative Arms had a better idea…
Switchblock gas systems are traditionally actioned on the gas block itself: There’s a little mechanical switch the shooter moves to turn the gas on or off. But that requires the shooter to move out of position to activate the button, which could be a problem if you’ve already lined up that perfect shot. Gas blocks also tend to get hot, making the switch painful to touch.
Innovative Arms has come up with a better idea: Turn the gas system off at the upper receiver.
By putting the cutoff switch on the upper, the shooter no longer needs to move out of position to operate it, and the switch itself will not be nearly as hot as if it were directly on the barrel. It also means the switch can be larger and easier to operate, and the design allows the shooter to tell with a single touch whether the gas system is on or off without needing to visually inspect it.
It’s an ingenious solution to the switchblock problem, but it does mean that you need a special gas tube to handle the pressure. At the moment they only offer carbine length systems, but they say they’ll be expanding into other lengths as well shortly.