Here is how to calculate the special recharge cap for the weapon your using:
Full Auto Weapon Cap = 10s + Weapon Attack speed
Burst Weapon Cap = 8s + Weapon Attack speed
*Aimed Shot Weapon Cap = 10s + Weapon Attack Speed
*Flingshot Weapon Cap = 3s + Weapon Attack Speed
*From talking with people I'm guessing the caps for aimed shot and fling shot are somewhat like this but I can't be 100% sure as I haven't tested it myself.
Now I'm fairly sure the final cap gets rounded somehow so that it's a whole number. However, weapons with .5 in their attack (like Augmented Hellspinner) still seem to round down and has a 9 second burst recharge without skill lock. However Caterwaul has .9 in it's speed and seems to still round up so I'm still unsure of how the rounding works.
This is of course without any skill lock at all. Special recharges can still be brought below these caps using -skill lock equipment.
Weapons used in testing:
Augmented Hellspinner - 1.5 second attack speed (used for testing burst)
Augmented Hellfury - 2.5 second attack speed (used for testing burst)
QL 200 Perennium Blaster - 1 second attack speed (used for testing full auto and burst)
QL 169 Spastic Assault rifle - 4.03 second attack speed (used for testing full auto and burst)
QL 236 Spastic Assault rifle - 5.04 second attack speed (used for testing full auto and burst)
QL 200 Caterwaul - 2.9 second attack speed (used for testing aimed shot)
QL 199 Ithaca Snakemaster - 1 second attack speed (used for testing aimed shot)
QL 260 Massive Bolt Charger - 1 second attack speed (used for guessing fling cap)
EDITED: Just to clarify what I'm talking about is the limit to which you can reduce your special recharge. Not the method in which the recharge is calculated. This is the recharge time you will get if you had 10,000 skill in the respective skill, the actual skill needed to get your recharge to this point is shown in a thread listed in the soldier resources thread.