Fair warning, you are standing on the precipice of a very deep rabbit hole :-). My Dad was a 're-loader' (loaded his own ammunition) and molded his own bullets and had charts and graphs for an amazing set of things. I even built him a chronograph so that he could "know" the speed of a bullet as it left the gun.
Given that a 'zeroed in' sight will account for the drop and so points the barrel up slightly, some of the energy in a shot goes to lifting it "up" before it starts falling down. You might think that would make it take longer, but it's small. The sin of 0.5 degrees is only .00873 so less than 1% of "heading up" before heading down. The more 'up' you point it, the bigger the difference. But as the author points out, the impact of various factors varies. Dad was happy he could put three rounds from his 30-06 into a 3" target circle at 200 yds.
That's a bit of a mistaken model, the bullet never rises above the boreline of the gun, the scope or sights are just angled down relative to the bore line to intersect the bullet trajectory at a particular point further down range. [0] The effect is larger if your scope is higher above the bore axis, because it requires you to point down more on the sight line to have the same zero, or if your zero is particularly close or far, for most rifle rounds and gun configurations 100 yard zeros tend to be all drop (the combination of realistic height over bore and bullet trajectories just work out that way).
If the sight is angled down relative to the barrel, the barrel is angled up relative to the sight. But which is angled "straight"?
The shooter aims with the sight, so if the target is level with the shooter's eye, the sights are level and the barrel is pointed (ever so slightly) up.
This means you are basically correct, in that the boreline is always pointed higher than where the bullet actually is (setting aside any lift the bullet generates, but that is a lot of detail to get into). However, the bullet does often move upwards relative to the ground (for some distance) since people are often aiming almost level to the ground. So in that sense, the trajectories are not "all drop". That is why I think you are being downvoted.
Yeah, should have said all drop relative to the point of aim/sight line I suppose, wrote for an audience more familiar with guns than HN probably is. Things are usually reference relative to the sight because that's what you're aiming with so movement relative to that is how you'd adjust your aim to actually hit the target.
There's not really any mechanism for lift though, the bullet is not an airfoil and is traveling directly into the airflow so there's not going to be any lifting body effects either while it's in stable flight and after that it's tumbling so there might be some then but it will be chaotic and inconsistent and you're just as likely to have it pushed down if the tail is up.
GP clarifies "the bullet never rises above the boreline of the gun" which tells me he might have thought that Chuck was saying the bullet literally goes up after coming out then comes down, instead of the boreline being pointed up relative to the pointed-down sightline.
Given that a 'zeroed in' sight will account for the drop and so points the barrel up slightly, some of the energy in a shot goes to lifting it "up" before it starts falling down. You might think that would make it take longer, but it's small. The sin of 0.5 degrees is only .00873 so less than 1% of "heading up" before heading down. The more 'up' you point it, the bigger the difference. But as the author points out, the impact of various factors varies. Dad was happy he could put three rounds from his 30-06 into a 3" target circle at 200 yds.