when they notice that their sentry has been silently-shot. They aint going to ANYTHING but dive for cover, eat-dirt and PRAY. shtf, nobody's going to HAVE the ammo to spray hundreds of rds into the brush or darkness. First time you do this, with 308, you won't have any ammo LEFT to do anything else with. Maybe YOU would be stupid enough to fire a silent .22 at a sentry, without having both cover and a couple of SOLID escape routes, but intelligent men won't.