Nice job, Daubs. I like the lightening holes, since weight is one of the main reasons for a carbine. These DCM tubes weigh a ton. They're all heavy gauge steel and stainless, and I'm all old and tired.
I'm going to try and get around that on a 14.5" pencil-barrel midlength by silver-soldering a handguard-length piece of thin-wall aluminum tube into the front hollow of a stock barrel nut. The delta ring holds the rear ends of the plastic handguards to the nut during recoil and indexes them. Then jam a handguard cap with an oversize barrel hole onto the front of the handguards with some Loctite.
Don't know if it's just a happy coincidence, but 1-1/4" OD tube is a perfect size, both in the barrel nut and under the front ends of the handguards with the heat shields in, for a rattle-free fit. Need to notch it up front to make room for the gas tube.