>>5114685
Every 20 or 30 rounds (depends on what you like), it displays a brief reload animation, just moving the gun to the side of the screen, swiftly swapping the magazine for a new one, then back in action and ready.
Think the reload animation for the pistol in Duke Nukem 3D, it's done in a second and you're immediately back to shooting.
What this does is to let you still have a volume of fire with the gun which is good, but it is limited, and it cannot compare to the volume of fire of the chaingun, which can fire its entire ammo pool uninterrupted, no pause for reload.
If you want the assault rifle to remain relevant and not be made fully obsolete by the chaingun, make it so the rifle has much less spread than the chaingun, so it's better at hitting at long ranges, never shooting wider than say, "2, 2", whilst the chaingun shoots at least double that.
Potentially, add an ADS or scope which lets you fire single shots in semi-auto only, but with perfect precision, "0, 0".
Another thing you can do is to give the rifle a grenade launcher, letting you firing a bouncing grenade that explodes on contact with enemies, with some decent range and damage, but it needs a reload after each shot.
This makes it more useful overall, but it has a rate of fire limit to its launcher, to not make other explosive weapons obsolete.