Try this.

ar-15-platform-barrel-whip-discussion

The barrel whip he shows is perceived at the muzzle and it looks pretty noticeable at that position. His overall conclusion (that the muzzle device is applying the force that deforms the barrel) seems reasonable and is supported by his testing with other devices.

So if you're going to run a comp, you're more likely to see up-down deflection than if you run a symmetrically ported flash hider. But either way, the barrel vibrates some and probably moves in all directions after the initial push.

Extrapolating to how much movement you might see at the gas block, there are too many variables even beyond the muzzle device design to even consider making guesses. Flex in the receiver itself, looseness in the fit between the receiver and barrel extension, contact design of the barrel nut and physical flexibility of the barrel itself all probably contribute to the amount of movement you might see. Case in point, I can create that 1/16" deflection (at the gas block) of my Adams Ultralight middy-barreled build using downward pressure on the flash hider. All of that flex appears to occur in the barrel only, but I knew it could be whippy when I chose it. A 16" Rainer medium profile barrel shifts far less under light pressure but does move. Who knows how much it really moves under fire?

IMO, given your situation (where the upper/rail has value far beyond simple replacement cost ), I would be looking at other gas blocks with more than 1/16" clearance.

D.