But we still limited full elevation to only 42 degrees, though the guns are designed to elevate 45 degrees for maximum range, in order to take excessive pressure off the roller in the roller path. If I recall, in WW II, the USS Texas had a problem with her rollers flattening out when the guns were at too high of an elevation.
But I've also been told that, during the Korean War, one of our Iowa class Battleships was able to get her gun barrels raised to 45 degrees relative to the tangent of the Earth's curvature. This was done by deliberately positioning the ship alongside an underwater sand bar and ballasting down onto the sand bar listing the ship at least 4 degrees. But I haven't seen any official report on that though it is perfectly logical.
And for the last part of your question, ummm, it might be possible for the muzzle blast of an adjoining barrel to activate the base fuse of a shell just a fraction of a second ahead of it. I don't recall which book I have that shows a photo of one of our Iowa's firing a full salvo but you could see the shaving brush fan out of black smoke from a warhead detonating in the air.
Hard to say which is better. The shell going off after it's well away from you or having the problem the "Mamie" had during the battle of Casablanca where many of the fuses screwed themselves out half way to the target.