Do some guns knockback/stun?

Question

I have noticed that when using certain weapons against enemies that the enemies seem to get stuck in a 'taking damage' animation while I'm firing at them. This is most noticeable with the chain gun against enemies like imps, where the imp will make a variety of 'taking damage' noises in addition to their animation.

This is to be expected, afterall I am shooting them in the face with a chain gun. However, I have noticed that on some of the bigger enemies that while ever I keep hitting them, they do not attack. They'll keep moving around and if I stop firing them will attack me immediately, but if I start shooting at them again they'll resume their 'taking damage' animation and sound loops and stop attacking again.

I have noticed that this doesn't happen with all guns, most notable the pistol (most enemies don't even do their 'taking damage' animation) and the BFG9000 (due to the massive firing ramp up time) but with weapons like the chain gun it seems to be possible to stop an enemy from attacking you for as long as you have ammunition.

Do some of the weapons in DOOM knockback or stun enemies?

Answer 1

The chance of "stunning" an enemy is called "Pain Chance". Each monster has a certain chance that they'll enter a "pain state", in which they flinch and stop moving and attacking, each time they're damaged. This chance is fixed, regardless of how much damage is inflicted, and depends only on the type of monster that was hit. For example, Lost Souls always flinch; pinkies flinch around 70% of the time; and the Cyberdemon flinches about 8% of the time.

Each projectile fired by a weapon triggers a separate roll for pain chance, so rapid-fire weapons (like the chaingun, plasma gun, and chainsaw) have the most chance to inflict pain state. The shotguns also roll separately for each pellet, so they're effective as well. Weapons firing a single projectile, like the pistol, rocket launcher, and fists, only roll once, so a pain state is much less likely. (The BFG does damage on impact, plus additional damage with "tracers" that are cast from the player's position in the direction the BFG was fired. Enemies in the path of these tracers tend to get hit multiple times and frequently flinch as well.)

Sources: http://doom.wikia.com/wiki/Pain_state and http://doom.wikia.com/wiki/BFG9000

Answer 2

Yes, some weapons stun enemies. The chaingun and chainsaw specifically.

http://www.giantbomb.com/doom/61-7326/