If you have the standard M5 upper, any hand guard compatible with DPMS ‘high’ will work. If you have the M5E1 enhanced, the choices are limited to what Aero offers and just a couple other manufacturers that make products for that specific receiver. Availability is spotty at best for nearly everything handguard related on this platform, as demand is still off the charts. Many guys are finding success by putting their email on numerous notification lists with vendors. Having said all that, I’m going on week 8 waiting for a specific handguard I want that was supposed to be 2-4 weeks. Last part needed for the build, and it’s aggravating.