How did the Mk. 16 6"/47 guns achieve their high rate of fire?

When firing, these weapons were described as being equivalent to a 6" 'machine gun;' for example, during a firing trial in the late 30's, USS Savannah(CL-42) was reported to have fired an astounding 138 rounds in under a minute, truly impressive guns, and as a result, light cruisers were found to be more effective in the close range night battles of Guadalcanal and the Solomons than heavy cruisers. So, what made their prodigious rof possible?

 

It isn't the ultimate referance but navweapons is a good place to start on this sort of question. SEe:
http://www.navweaps.com/Weapons/WNUS_6-47_mk16.htm
One clue is in the first paragraph:

and later on:

Since Savannah was a Brooklyn class she had 15 guns and their rate of fire is listed as 8-10 rounds per minute which suggest she should have been capable of firing 120-150 rounds per minute so 138 is certainly reasonable.

If we look at the British equivalant http://www.navweaps.com/Weapons/WNBR_6-50_mk23.htm
we find:

Yet it's rate of fire isn't much less at 6-8 rounds per minute.

Looking at the Japanese equivalant (rated at 5-6 RPM) http://www.navweaps.com/Weapons/WNJAP_61-60_3ns.htm

It's also worth noteing that the US 5"/38 was rated at 15-22 rounds per minute but the HMS Dehli managed to get 25 during trials with hers. See http://www.navweaps.com/Weapons/WNUS_5-38_mk12.htm

 

I'm curious if our heavy cruisers could have achieved a higher rate of fire if they used the same loading system, and made them more effective in night battles?

 

With the same system, it would be very doubtful. The only increase in 8-inch RoF was with the introduction of the "automatic" loading system of the last heavy cruisers, the Des Moines class. It also cane at a great increase in turret weight, the Des Moines' turrets were about 50% heavier than those on the Baltimore class - 451 tons vs. 303 tons.

You would also have took look at how fast the shell and charge hoists could move their respsective cargo from the magazine to the turret - this is what hampered the firing rates of the Japanese Mogami class.

 

In regards to that Houston apparently exceeded the spec for 8" rate of fire early in the Battle of the Java Sea.
http://www.navweaps.com/Weapons/WNUS_8-55_mk9.htm
Contains this somewhat cryptic note:

I suspect that adopting the superheavy rounds wouldn't have improved the rate of fire without substantial changes.
This link gives at least something of a description of the Des Moines class guns:
http://www.navweaps.com/Weapons/WNUS_8-55_mk16.htm

 

NavWeps is definitely a good site to learn about the technical details of ship-borne weaponry.

 

I had heard that auto load systems increased turret weight, an unfortunate consequence for enabling heavier caliber vessels to shoot faster.