I have 5 Vortex Viper PST Gen 1's. All mine have Zero stops. They use a shim system. So maybe yours does have ZS and you just haven't set it up. Or maybe yours is not a PST. IMHO, the Gen 1 PST's are one of the best values in scopes out there, and I own some much more expensive scopes. For $5-700 on the used market, you get 6-24x, FFP, good tactile turrets, Zero Stop, excellent reticles (including Christmas tree), illuminated reticles, lightweight (23 oz), and of course an unbeatable warranty with a 100% American company. I think the used prices are artificially low due to internet bashing of Vortex by naysayers, similar to what I hear about the 6.5CM. Meanwhile, myself and others that try stuff for ourselves quietly reap the benefits.