The 20 inch barrel will definately NOT give you maximum velocity in .223. Get the 24 or 26. If I remember right the difference in 2 inches of barrel length is around 100fps. That's not a whole lot. If you're just going to be sitting blasting varmints and such or just want maximum velocity numbers I would go with the 26. But if you will be carrying it a lot I would go with a 22 or 24 inch barrel. Any of us who have been in the Army or Marines can attest to the accuracy of the .223 in relatively short barrels. We regularly hit targets out to 500 meters with those short 16-20 inch barrels. But then accuracy wasn't your question. Sorry got a little off there.