An assault rifle can fire at the same rate as a light machine gun because they both use the same intermediate cartridge.

1. Cyclic rate vs. sustained practical fire — two different measures

Rate-of-fire literature separates cyclic (mechanical) rate from sustained, practical firing, and that distinction matters here: assault rifles and machine guns can have overlapping cyclic rates — typical assault-rifle figures of 600–1,100 rounds per minute and machine-gun ranges that begin in similar bands show overlap — but sustained rates are limited by ammunition supply, barrel heating and intended employment, meaning assault rifles "rarely expend ammunition at the same rate as light machine guns" in practice ^[1].

2. Cartridge commonality is necessary but not sufficient

Both modern assault rifles and many LMGs may fire intermediate cartridges (the design choice that defines the assault-rifle class), and that shared cartridge simplifies logistics and allows similar muzzle energy and recoil characteristics ^[3]. However, cartridge type does not determine feed system, barrel mass, cooling or receiver strength — all of which dictate whether a weapon can actually sustain high rates of fire without failure or loss of accuracy ^[2].

3. Design choices that make LMGs sustain fire

Light machine guns are adapted from or designed beyond basic rifle architecture to enable longer bursts: heavier or quick-change barrels, more robust actions, larger-capacity feeding (belt or high-capacity drums or box magazines) and bipods for stability, all intended to permit sustained suppressive fire ^[2]. These mechanical and ergonomic adaptations, not the cartridge alone, enable LMGs to deliver longer strings of fire and higher sustained volumes than a standard assault rifle built around the same intermediate round ^{[2] [1]}.

4. Heat and ammunition logistics are fundamental limits

Heat buildup is one of the major practical constraints on firing rate: a machine gun that must fire long bursts is designed with barrel mass, cooling or quick-change barrels to manage overheating, whereas a typical assault rifle generates heat rapidly and is not built for protracted continuous firing ^[1]. Ammunition feed is the other obvious limiter — belt or large-drum feed systems used on LMGs sustain fire that box-magazine-fed assault rifles cannot match without near-constant magazine changes ^[2].

5. Where the claim is partially true — overlapping cyclic rates and hybrid designs

The claim has a grain of truth in that some assault rifles and LMGs exhibit similar cyclic rates mechanically (Wikipedia cites overlapping ranges and notes cyclic rates for assault rifles and machine guns can sit in similar bands) and some modern squad automatic weapons blur the line by accepting standard rifle magazines or using the same cartridge as riflemen ^{[1] [2]}. There are hybrid designs and doctrine choices that intentionally align a squad's automatic weapon with its rifle cartridge to simplify logistics ^[2].

6. Verdict: cartridge alone does not equal identical firing capability

Concluding cleanly, sharing an intermediate cartridge does not make an assault rifle able to fire at a light machine gun’s effective rate in combat; mechanical design choices, feeding systems, barrel and cooling solutions, and doctrine determine sustained and practical rates, and while cyclic rates can overlap, assault rifles "rarely expend ammunition at the same rate as light machine guns" in real use ^{[1] [2]}. Sources show both the technical overlap and the decisive distinctions, so any claim equating them based solely on cartridge choice is incomplete ^{[3] [1]}.