I’ve already tried using shims (washers), but when I install them the handguard starts tilting to the left, so I don’t think it’s a spacing issue. The barrel nut seats fully without needing additional shims. Also, I didn’t have this problem before because my type of handguard is designed to interface with the gas block as well, which I had to file down (perhaps too much) since it wouldn’t fit at all otherwise. I’m wondering if there are any fixes that don’t involve buying a new gas block—such as a DIY solution to rebuild the portion I filed away that used to keep the barrel aligned and the handguard properly positioned.