This is the longest of my three posts. My apologies if I am making a mistake in posting these comments.
Notes: "Smurf" is an acutal naval researcher and author. I know he has had a number of articles in the Warship Annuals, mostly about RN cruiser designs of the last century. MJBurmaster is a retired naval architect, I believe.
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Posted by Smurf:
If you fire again before you know whether the range etc is right, you waste very expensive ammunition. 8" and 6" is a lot cheaper than 16" 18"
Des Moines 8" is to fire at destroyers, short range
Worcester 6" at aircraft, short range and a bit of a scattergun effect.
BBs firing at 7-10 miles there's not a lot of point in firing more than about 2 rpm. If you do there's likely to be lower percent hits and you will need much bigger magazines. Don't forget the target moves.
Shore bombardment is another matter, but you don't need a 30 kn BB for that.
Des Moines size not due to bigger turrets, but bigger ammunition spaces and the armour to protect them which drives up the power needed etc.
Posted by Marek Gutkowski (Russian, I believe)
I meant to say that your guns well overheat fast.
100 rounds at RoF 2rpm gives 50minut sustaind fire
100 rounds at RoF 6rpm gives 16minut sustaind fire and by that time your Guns have to cool off and you diss engage.But is not a big problem give that late 1940' BB role is to protect the carries from heavy enemy wessels.
Sending at your enemy 900 rounds in a time in wich they sends you only 288 round gives you a big advantege.
Higher RoF is like having more guns, so a 35000t ship with 6 automatic 15'' gives fire power of 12-15 normal guns.
An egzample South Dakota with 6 automatic 16'' in twins(lets dont forget the higher weight of automatic guns) only dubling not tripling HoF per gun.
Fires not 18 round per minut but 24rounds.the ship isnt bigger that others but hase more fire power. althou 6 more rounds per minut isnt all that impresing in 10minuts its 60rounds more.(240vs180)
In battle line tactics it gives you following in ten minuts you fired more that means,acording to N-sqeard law,you hit more now your guns are overhited they nead to cool of a bit you RoF drops to 1 or 2 rpm.
The enemy hase a dilema you made more damege to him that he had done to you.He can either reatret and lose the battle or continue on still knowing that even thou your RoF droped dramaticly if the battle goes hard for you your captains still have an option to puch ther guns over the seafty margins firing the guns at higher RoF destroying the guns in the proces(my friend that were in the altylery sead that thers guns had 2 HoF susaind harasing fire or short rapid fire,althou they were thout that in an event that the enemy is charging at the they are to fire in rapid fire till the gun turn red).
Modern Sowierenny class Destroyer has only 4x130mm but high RoF of its guns give it fire power almost equal to Atlanta class CLAA.
Posted by Smurf:
But it only gives a 6 shell salvo, after which the target has moved
The reason for more guns is not just greater weight of broadside, but to increase the chance of hitting, given that there is an inevitable spread in the salvo due to small differences in manufacture of shells, quality of propellant etc. No 'next shell' goes exactly where its companion goes. You fire 10 or 12 rather than 6 so that you have a better chance of hitting. You fire salvos of half your guns to obtain in effect greater rate of fire with the same (smaller) number of shells arriving at once.
So a 6 gun auto ship firing broadsides puts down the same number of 6 shell groups as a 12 gun ship firing 6-gun salvos. With half the rate of fire per gun, because salvos are fired twice as often as broadsides, the 12 gun ship and the 6 gun auto then have the same chance of hitting overall.
But the 12 gun ship can fire if desired 12-shell patterns and increase its chance of hitting with one attempt, if you think that's the only chance you might get. What you do depends on range, visibility (pre radar) whether it's line of battle or single ship action, smothering or armour penetrating fire etc.
You can't really go to 3-gun salvos - chance of hitting at all is so small
Also, simpler mechanism is generally more reliable - hence sticking to twin turrets against triples or quads. Auto loading involves more mechanism and so increases the chance of mechanical failure which decreases the chance of hitting. If you don't fire, you can't hit
Posted by MJBurmaster (subject: Loading Equipment):
whilst all involved are thinking about automated equipment to increase ROF, let me point out a very practical reason for increased, not full, use of machinery, and that is the weight of the "things" being used.
You don't want full automation without alternatives. For example, it is quite possible to lift a 16" shell with cable and tackle provided you have suitable passageways. But in a sea state above the 3/4 level or such then things begin to get a wee bit chancy. Not that a shell will fuze, but certainly shell utility is reduced when beaten up on various objects. (If you think a shell is so solidly built to defy such problems....

) Add to that personnel "discomfort" (such as getting equally banged around on steel ) and increased mechanization is required.
One could have an argument which is better, electric motors or hydraulics. I would say that electric in my experience is better because hydraulics do take up more space and can't get moved about as easy as a 440 cable. As for the disruptions caused by shock or water, let's just say that shock will dislocate any system and if water is entering the barbette ring, you probably have the makings of a very bad day in any event.
Posted by Aglooka:
The heavy German guns didn't use brass cartridges in its usual meaning. German guns didn't have gas check pads (sliding breech block) and a short brass cartridge containing the aftermost charge had a "cartridge", in front of that were the usual silk lined powder bags. The cartridge was used to seal the breach, not to contain the (majority) of the charge.
Im' skeptical about the feasibility of brass cartriges for bs size guns. How thick would the cartridge wall have to be to maintain the mechanical integrity of the cartridge as it was being handled ?