Mellee damage by fists and gun butts

I'm curious why there is an option to hit in mellee damage by fist (if you armed pistol or one-handed rocket launcher) and butts (if two-handed guns), but no info about ammount of damage and attack speed?
I already test and found that it around 19 damage from hit to non-armoured targets like civilians. Also time between shots is around 0.5-0.7 sec for fists and 0.9-1.1 for butt hit. I test it with 0 points in mellee stats.

If you guys found something it will be interest to know (does mellee stats affect range weapons if use it like mellee etc). Feel free to share