I do not know if this bug is exclusive to guns. They are the only weapons I've been able to test for this issue. Testing on other weapons with a reload- + attack-speed of less than 3 sec would be desireable.
Reproduce by:
1a. Load the attacher savegame.
1b. Create a Ranger with max dex and proficiency in pistols. Level him up enough to aquire the gunnery passive. Aquire 3 pistols, and equip 2 in one set and 1 in the other.
2. Enter combat with the 2 preloaded pistol set activated.
3. Fire the initial salvo with a total combined attack-speed of 1,3 sec (in my save, I'll be defaulting to my saved numbers from her on), and observe it working in approximated accordance with tool-tips.
4. Activate the pistol-modal for a combined attack-speed of 2,5 sec. Observe it fireing at a frequency of ~3,5 sec, not in accordance with tool-tips.
5. Switch to single pistol and activate the pistol-modal, for a combined attack-speed of 2,8 sec. Observe it fireing at a frequency of ~3,5 sec, not in accordance with tool-tips.
Attached files:
https://www.dropbox.com/sh/wm91ijmhuezfi62/AAAeNnz2SCTSifAFf24-hHgRa?dl=0
output.log
dxdiag
save
EDIT
I've made a thread for an attempt to gather information on what weapons or means of attack are affected by the bug:
https://forums.obsidian.net/topic/98628-a-call-to-testing-actual-attack-frequency-caps/
EDIT
Weapons/Attack-types known to be affected:
Pistol
Blunderbuss (from Zzz)
Weapons/Attack-types known to not be affected:
"Tested on Dragon's Dowry + Blazing Fury. Works as intended, get ~3s time between attacks." (From Helar)
Sabre, bow and arquebuse (from Zzz)