when I was looking into carbon fiber hand gaurds I found they epoxy to the barrel nut like this: https://www.midwayusa.com/product/313249/dpms-free-float-tube-handguard-lr-308-rifle-length-carbon-fiber-matte thats how the dpms ones were when I was looking at them, now I see they make them with Allen machine screws too, but I'm betting yours is epoxied to the barrel nut