burst chaingun-whacked4

Basically, you'd just need to use additional frames between the "FireCGun" action but before the "Refire" action. The chaingun shoots twice by default, but by reallocating some other frames, you could make it shoot a 3rd time, then call a frame with a ~20 tic duration as the "cool down" between bursts.

Since examples are often easier than explanations, here's an old wad called CoopBuild which replaces the pistol with a burst-fire rifle. If you open the included DEH file in WhackEd, you can see how it works - from the moment the player clicks "fire", it goes through many frames, ending with a 20 tic cooldown frame, before it finally goes back into the "WeaponReady" state (which means the gun has stopped firing, and is ready to be fired again).

Hopefully the included example makes it clear - make sure you follow each frame, and pay close attention to the "next" frame to see all that happens when the player simply fires the gun.

coopbuildlm.zip

thanks @Doomkid it really helped!