Just picked up a viper 1-4 that's going on top of my 11.5" SBR.  What would the factory's recommendation for the zero using .223 ( mostly federal factory ammo).  Is it still the 100yd zero?

Truth be told, there is no hard and fast answer to this question. If it were me, I would zero based on what my applications for the firearm were. If I were using it for home defense, etc. I might zero for 25 or 50 yards. If I were hunting or plinking with it, I might look at 50 or 100 yards for a zero. If you ask different people, you will get all different answers, but I personally prefer a 50 yard zero on a lot of my ARs. a 50 yard zero tends to be roughly equivalent to a 200 yard zero and will be close enough at 100 that it won't matter for most people's applications. Also, a 50 yard zero is a little easier to do well with low magnification than a 100 yard zero is. Thanks and please let me know if you have further questions. I would be happy to help.