People get real wild with the filament stuff for sure. I have one of these same builds in matte PLA, and PLA-F. My Modelo has silk PLA and normal PLA parts on it that are all original 2000 rounds later.
I don't recommend people use these weird materials, but I like to put it out there for everyone just as another data point.
My barrel nut for my 21.5" m4gery is this same PETG-GF and it's been working great. I broke my PLA+ barrel nut.