Comments by "Steve Valley" (@stevevalley7835) on "Battleship Guns of WW2 - A series of tubes" video.

@genericpersonx333 a higher velocity shell, for a given range, will travel in a flatter trajectory, so it's chances of hitting are better because the distance between where the shell would hit the top of the hull and where the shell would hit at the waterline is longer because the shell drops less per unit distance. (there is a name for that zone, but it isn't coming to mind right now) If you want to go for a deck hit, then you want to fire at a lower velocity so you can fire at a higher trajectory. But, with a higher trajectory, the chances of a hit are lower because the shell sinks at a higher rate. The travel time to distance is listed in the gunnery tables. A USN 16'/45 firing with a reduced charge yielding a muzzle velocity of 2000fps at a target 23,500yards away: angle of departure from the gun 33 degrees, 20.4 minutes. Time of travel: 58.25 seconds. Angle of fall: 42 degrees 58 minutes. Firing the same gun with a full charge, yielding a muzzle velocity of 2600fps. at a target at the same range of 23,500 yards gives the following trajectory: angle of departure from the gun 15 degrees, 35.4 minutes. Time of travel 38.44 seconds. Angle of fall 22 degrees. 24 minutes. As you said, firing at a higher velocity makes it easier to hit the target, but, if the ship has heavy deck armor, and you hit on the deck, at 22 degrees, the shell may ricochet off. Drop a shell on the deck at 42 degrees and it punches through.
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@jarmokankaanpaa6528 I agree with everything you say, in general. There are circumstances where a deck hit might be easier or preferable. In the case of Hood, iirc, Hood was heading, more or less, toward Bismark, so the target presented by the hull would appear smaller, a shell would hit at an angle, limiting it's penetration, and there was no way to mitigate the angle of impact. But the deck target area offered would be the same as if Hood was on a parallel course. The armor penetration table for Bismark's guns doesn't go below 20 degrees, because a hit at that angle would ricochet off, but there is a way to mitigate that angle of impact issue on a deck hit: use a reduced charge. My theory is that Bismark's gunners knew their business, only loaded the main charge in the guns, fired at a higher angle, going for a deck hit, and the eyewitness testimony by Captain Leach of a deck hit is correct. Unfortunately, the extracts from USN gunnery tables that I have access to are partial, so I can't find the exact angle of fall at the range, approx 19,000 yards, where Hood was hit, and the characteristics of Bismark's guns would be different. As close as i can come is a USN 14" at 14,500 yards: angle of fall at full charge 12 degrees, 5 minutes. For a reduced charge: 20 degrees 53 minutes, which is getting to the angle where a shell could punch through Hood's deck armor. The actual shot being at a longer range, the angle of fall on Hood would be greater. On the side hit issue, the term I could not recall last night was "danger space". For that same USN 14" the danger space with a full charge and a 20' high target was 31 yards. From the drawings and pix, Hood appears to have had between 25 and 30 feet of freeboard midships, so the side hit danger space would be correspondingly larger. Hood's beam was 104ft, or a bit over 34 yards. Given the angle Hood was at, the effective range difference between the near side and far side of the deck would be quite a bit larger than 34 yards. Captain Leach testified that Bismark was firing half salvos, and two hit short and one long, or one short, two long, he didn't recall which, and he had an "impression" the fourth shell landed near the mast.
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@briancox2721 that was the day the USN discovered "copper choke", where copper from the driving bands on the shells builds up in the bore to the point where it impedes passage of the shell to the point where pressure in the tube is high enough to burst the gun. After that, the USN started issuing cleaning tools to remove the copper buildup.
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@jakemillar649 it would probably asphyxiate or burn everyone in the turret to death. There was a case, prior to WWI, when the propellant ignited as you suggest. At that time, there was no air purge system in guns. The gunners were instructed to look in the tube for embers and flames, before ramming the next round. On a 12" four propellant bags were used, rammed two at a time. The gunners rammed the first two bags, and ignition was almost instant, as inspection after the fire showed the rammer was still in the fully extended position. There were no safety shutters on hoists then either. When the flames shot out of the breech, they ignited the other two bags that were still on the hoist. Hoists were not in enclosed trunks then either, so chunks of burning powder rained down to the handling room, igniting more bags of powder. Somehow, the magazine was not ignited, so the ship didn't go up like a Roman candle. Some 35 men died that day.
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@dmnorthwind9584 Guns can be relined. The usual procedure is to heat the outer jacket of the tube, while running cold water through the bore, to make the outer jacket swell and the liner in the bore shrink, loosening the old liner, so it can be pressed out. Then a new liner is inserted, and the outer jacket allowed to cool, which clamps the liner firmly in place.
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