Tried to install a free float handguard on one of your all's DT Sport Lites and found the barrel nut the tightest I've ever seen. As in, using an upper reciever block and the insert, tightened down in a vice, I first broke off a couple of teeth on the barrel nut. So this was the point of no return to me. I finally had to grind off the delta ring assembly and put a pipe wrench with a long cheater bar on it to get it to finally cut loose. I wish I'd have put a torque wrench on it, but I'm estimating over 230 pounds.
I didn't see any type of threadlocker and maybe a little bit of grease. This was a brand-new, unfired gun. Anyway, I had to put enough torque on it that the upper receiver itself is hosed. A bolt carrier won't slide freely inside it.
I've taken barrels off dozens of times with many other manufacturers costing much more, and never so much as put a scratch on anything. Never seen anything like this.