I have a DD MK18 5.56 upper. The bbl is CHF CMV chrome lined. My firing schedule is easy on the bbl, firing 5 shots and letting it cool to ambient temp while I shoot something else. Those 5 shots may be shot pretty quickly though. To date, I've fired 2369 jacketed rounds through it. I also measure my bbls for throat wear using a Brownell's bought TE gage.
The TE measurement from when it was new to 2369 rounds later shows NO wear! The loads I shoot the most are either W748 with 55gr fmj or IMR4895 with 50gr frangible bullets.
I will mention one "problem" with my upper. To reduce the muzzle blast on others shooting with me, I installed a Spike's Barking Spider. Like flipping a switch, I began to have failures to extract. In my opinion, the Spider was increasing the gas pressure on the BCG causing the rifle to cycle before the chamber pressure was reduced enough to allow extraction. Replacing the Spider with the MI Blast Diverter restored perfect functioning and reduced muzzle blast. MI had told me their Blast Diverter would not increase the gas back pressure. Other linear comps might work as well.