I am new to all of this just so you know, but I also built a SPR/DMR for my first and probably last rifle. After reading around and antagonizing for weeks, I ended up going with a Daniel Defense V7 PRO as the platform for it.
The Barrel being the main reason, but man are there a lot of reasons for it, such as the entire thing, BCG, upper, barrel, everything is rated for full auto and accuracy, its a work horse.
Without sidetracking from your question about barrels too much theirs checks every box, - 4150 Chrome Moly Vanadium Steel, Cold Hammer Forged, 1:7 Twist, 18" S2W Profile, Chrome Lined, Mil-Spec Heavy Phosphate Coated, and HP/MPI Tested
It's a really nice barrel and barely weights more than the 16". Now since you are asking about uppers, theirs is also really good - Mil-Spec with Indexing Marks and M4 Feed Ramps. CNC Machined of 7075-T6 Aluminum, Type III Hard Coat Anodized
Another great thing is that they cold hammer forged the chamber when they make the barrel and marry them, it's oh so nice. So, I know you can buy their barrel stand alone, but you may want to look into seeing if you can purchase the upper and married chamber with it. I'm not sure if that's an option, but you can't go wrong with that barrel and 18" is plenty since you are like me and running it suppressed. Remember that will turn your 20" into a 25 real quick and that is if you run one of the smaller suppressors! So I was more than happy with the 18" length since I was running it suppressed the velocity is still outstanding and I have a barrel that is only 20 and change suppressor included, just something to consider.
I will link this barrel resource that has to be the best one ever written out of everything I read it was the best. It might help you decide, but the DD 18" has my vote.
Choosing the right AR-15 barrel is a daunting task, so let me help break down everything you need to know to get started
www.everydaymarksman.co
