One big difference between Oswald’s USMC rifle qualification and his shooting Kennedy, is that USMC rifle targets then didn’t move. They were also at Known Distance, hence the term the ‘KD Range’. Oswald had more time for each shot in qualifying, than he did to shoot Kennedy. Even in ‘rapid fire’ stages, the shooter has roughly six seconds per shot, according to this table describing USMC Rifle Qualification: https://www.lejeune.marines.mil/Portals/27/Documents/WTBN%2520RCO%2520Databook.pdf
The USMC changed rifle qualification in, IIRC 2007, but it’s similar to what Oswald did. The target Oswald shot at in the USMC, for slow-fire stages was, AIUI, either a 12 inch black bullseye for closer targets (200 and 300 yds), or a 20 inch bullseye for further targets (500 and 600 yds). Known as A and B targets, as seen here: The 5V targets - CMP Forums The rapid fire stages were shot with a ‘Dog’ target, meant to mimic a silhouette of a prone enemy soldier. Dimensions and an image of the targets here: http://i139.photobucket.com/albums/q314/number1gilla/boomsticks/USMCKnownDistanceTargets.jpg Along the way, the USMC added a man-shaped silhouette to the old A and B round targets and the Dog target silhouette.
The point of all of that was to point out that Oswald, and every other Marine, had experience shooting at quite small, head and shoulders-looking targets, at ranges far in excess of those in Dealey Plaza.
However… He didn’t have as much time to make the shots. He didn’t know exactly how far Kennedy was away. His target was moving. Due to the telescopic sight on his rifle being shimmed incorrectly and out of adjustment, he was forced, in my, Vincent Bugliosi’s, and Tom Clancy’s opinions, to use the poor, open iron sights instead. While his USMC qualification was also done with iron sights, the aperture sight on either a Garand or a 1903 Springfield (whichever rifle he qualified with) was far superior, precise, and easier to quickly use than the open notch rear sight on his 91/38 Carcano rifle. All of those factors would make the Dealey Plaza shots harder than qualifying, despite the much shorter range.
Considering that between drop and air movement a bullet can drift multiple feet from the target, it would be foolish to post a sniper on a 1000+ ft building and the question and discussion is basically nonsense. Put a few observers/spotters up there, or in a helicopter and have them relay the info to those closer to the target(s), yes. Endangering multiple others to get a single or multiple potential or real assailants is extremely poor defense/protection.
As for the bullet still being lethal after traveling 1000+ ft downward. Yes. As the Mythbusters proved, a bullet fired straight upward and having traveled thousands of feet, losing all it’s ballistic energy, upon return at terminal velocity can and has been lethal.
I’m referencing the OP’s first question: “1. Would a rifle bullet still impart enough velocity to be effective at that height towards a ground target?” by stating that even once it’s lost all it’s ballistic energy when fired upwards, it still can, be lethal in freefall. https://en.wikipedia.org/wiki/Celebratory_gunfire
A bullet fired down, up or sideways has enough ballistic energy to be lethal for well over a mile as evidenced by sniper long shots and shots taken at aircraft.
If it’s a .50 cal or .338, it’s going to be lethal for a lot farther than a mile. As mentioned, a Canadian Sniper scored a kill at 3.5 kilometers. A .50 caliber bullet remains lethal out to about 7 kilometers, but hitting anything at that range would be sheer luck.
Under 500m is no big deal for any good sniper, but I agree the winds around the building would add a lot of uncertainty to any shot.
As for Oswald, the schlocky conspiracy books always make that shot look harder by forcing people to try it by starting a stopwatch, then having them try to shoot 3 times in six seconds, while scoring the same type of hits. But that’s a bogus way to do it, because A) the clock should be started after the first shot is taken, and that first shot can have reasonable setup time. And B) demanding that there be a head shot isn’t reasonable, because Oswald may have just been aiming center mass and the head shot was ‘lucky’. When you change the task to be one shot at the shooter’s leisure, then two more shots in 6 seconds, the result of which is at least one fatal shot, pretty much everyone with any rifle shooting skill can do it.
I’d add 5.56 and definitely 7.62 to the ‘lethal over a mile’ category. Both will be subsonic before then, but 150 grains subsonic sounds a lot like a 9mm, 147 grain bullet at the muzzle. Which is obviously lethal. Hitting what you aim at is going to be a challenge… That said, old school military bolt rifles commonly had leaf sights calibrated for ranges in excess of a mile, for ‘volley fire’. How you emulated a machine gun with a rifle company when you didn’t have an actual belt-fed machine gun.
I think Oswald tried the scope for his first shot, missed hilariously—maybe hitting James Teague with the spall—and figured out the carbine’s sights were what to use. I think Oswald anticipated more movement on his third shot, where the Secret Service driver slowed to allow another agent to get onto the back of the limo, and that slowing turned another chest hit into the headshot. So it goes.
