The ammo regeneration in BL:TPS us a little weird, but by using Wilhelm’s Overcharge skill I have found some of the information.
Wilhelm’s Overcharge - +10 ammo regeneration per 10 seconds
(all values are per 10 seconds for simplicity)
SMGs - 120 rounds
Lasers - 110 rounds
Assault Rifle - 100 rounds
Pistols - 85 rounds
Shotgun - 50 rounds
Sniper Rifle - 30 rounds
Now, it seems that they have made new timers for ammo regeneration as shotguns would regenerate only 10 rounds using the old timers, which was 10 seconds.
I am trying to find out how the “timers” work for the +1 and +0.1 registrations but this is a good start.