U.S. Naval gun/caliber/bore question?

I have managed to get myself confused… O.K., some might comment that is not a difficult thing to acomplish…

I have looked around a bit, and I may well have simply missed the answer I seek, thus, I feel the need to ask:

I remember the larger guns on Navy ships refered to as “caliber”, such as a 3"/38 or 3"/L38 or 3/38 Caliber, meaning a bore diameter of 3", and a barrel length of 38 times the bore diameter, or 114" long barrel, (correct so far, yea?).

Now I see people making reference to “X pounder”, “X” being, what, the weight of the projectile? Does that actually designate the caliber or loaded shell with any accuracy?

Because… we had the 16" guns, which originally had a barrel length of something like 16"/L45 [720"] firing a 2,000 [?] pound projectile, and later it became a 16"/L50 [800"] firing a 2,700 [?] pound projectile, but we do not hear them refered to as a “2,700 pounder”.

In the Army, hallf a lifetime ago, we simply called it by caliber/gun, like a 155 Howitzer, 90mm Recoiless Rifle, 81mm Mortar, etc., SOOO much simpler!

If it can be explained without having to write a book, that would be nice, otherwise you can all just chuckle about me, and toss a few ‘Ground Pounder’ jokes around. After 61years, I am well used to it.