Back in my younger days I could load a 105mm tank cannon in under 4 seconds,...but if the monster was going down the tank trail it becomes a game of hit the jumping hole.

10 seconds sounds right for a boat on water.

Being a avid deck gunner (in SH3), I will frankly admit I have NO idea what my reloading time is. I play with default GWX3.0 settings, and I haven't seen any reason, (nor want to create any my myself) to change any of the settings.

The GWX3.0 team have done a very balanced job, within the limitations of the SH-3 engine.

GWX 3.0 no deck gun ammo
 

When checking my ammo (key i) everything looks fine but when I order my men to fire the deck gun they say that there is no ammo.

The AA works...

How can I fix this?

Assuming you're running GWX, you must manually click the HE shell icon to load the ammo into the gun before firing. Have you done this?

As Steve et al have already posted, there is a big difference between the questions

1. How fast can the crew fire the deck gun

2. How fast can the crew fire the deck gun accurately.

To fire the gun accurately, I would imagine that 20 seconds is not totally unreasonable. The gun may be able to operate much faster. I imagine that if accuracy was not a concern a good crew could fire it every 5 seconds... but they would miss.

There are a couple more parameters that need to be added into the equation.

How fast can the ammo be passed from the locker into the conning tower hatch and then onto the gun?

Also a good point. My research on surface ships over the years has turned up the interesting phenomenon that, unless the loading system is fully automated, there is always a difference listed in rates of fire before and after ready-use ammo is exhausted, with the latter usually being about two-thirds of the former. If it has to come from a remote source, rate-of-fire decreases dramatically.

Ive set mine to 7 seconds, i guess i should atleast double it.