I picked this one up 2 years ago. I haven't shot it over 50 yards yet. But, at 50 I'm pretty much using the same hole over and over. The price is right if you have an upper and a bolt laying around and you can do your own work assembling it.
https://www.midwayusa.com/product/1003430710?pid=577053That's a nice barrel. I have to ask, why only 50 yards? Are you limited to just a 50 yard range? Also, keeping in mind the op is looking for a "long range" upper. I don't really know how a rifle barrel shot at 50 yards would even apply to what the op is looking for... Fill us in please..