I have one PST, and thus far it has been pretty darned good. The best thing about it is it's light weight. I really like the PST Mrad reticle. But it has a 5 Mils per rev turret as opposed to 10 Mils on the SS, and it looses clarity at 24X o I turn it down to 22X or 20X.
But in the toughness category the SS is the clear winner over the Viper PST in my opinion.
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