I guess that would depend on which end of the barrel the RRT-3 is located...
OK, seriously... thats one HUGE light to strap onto your M4, however being an LED light and the fact that Jetbeam states that the RRT-3 is "Specially designed for Military, Law Enforcement, Self Defence, Hunting, Search&Rescue...etc...Stainless Steel crenulated bezel...can be used as a glass breaker or defensive tool...can utilize tactical pressure switch...etc" I'd say its pretty safe to assume it was designed to be small arms mountable.