IMHO,
I just purchased a SS Bushy H-bar and after shooting 100 rounds the handguard cap became loose, and the handguards wobbled considerably. I e-mailed Bushmaster and they answered me within 30 minutes with the following:
The front sight gas block pushes the handguard ring tightly into the step, machined in the barrel. The cap should not move. I can either send the upper back, and they will repair, or I was instructed to try tapping in the front sight taper pins, which should force the cap against the step, or to use 271 locktite (Red) and carefully put a drop or two between cap and the step in the barrel. I tried tapping the pins, but no luck. I used the locktite, and the cap is now tight. I also ran a bead of epoxy around the same area for assurance. I'll see if this holds the next time out.
Ted