The Rifle Tower

Hideous puns are one of my special skills, so I just thought I’d get that out of the way.

I like the idea that this is about witnessing something impossible, and I think there are more things to add: especially using existing tourism as a way to further ‘parasite’ one thing off another.

But I also think it is important that it is presented in a thoroughly convincing way [which is why Jimmy’s drawings need to include evidence of physical feasibility]. So I have decided to try and solve the height question as realistically as possible.

Most of the online info is related to terminal velocity, where people are interested in calculating how much force bullets exert on the way down (can bullets kill you when they fall to ground after being discharged kind of thing).

Physics and Maths forums have interesting stuff relating to height, but it looks like the only accurate data is mathematical and relies on a vacuum. Here they are talking about enormous possible heights. But one poster says (my bold):

to the two guys with the math formula's "stop" you are not going to find a bullet that 45000 meters!!!!! ever!!!! 50km is roughly 32 miles, large Field Artillery can't reach that far. A large caliber rifle like a Barrett .50 sniper rifle will go about two miles, straight up, a little less. Small caliber rifles like a M-16 with a .223 or just a bit bigger .308 will go between 550-1000 meters. really small caliber like a .22 will be about 300 meters.

This is the best I have found as far as actual height is concerned (about 2/3 of the way down the page):

In 1920 the U.S. Army Ordnance conducted a series of experiments to try and determine the velocity of falling bullets. The tests were performed from a platform in the middle of a lake near Miami, Florida. The platform was ten feet square and a thin sheet of armor plate was placed over the men firing the gun. The gun was held in a fixture that would allow the gun to be adjusted to bring the shots close to the platform. It was surmised that the sound of the falling bullets could be heard when they hit the water or the platform. They fired .30 caliber, 150 gr., Spitzer point bullets, at a velocity of 2,700 f.p.s. Using the bullet ballistic coefficient and elapsed time from firing until the bullet struck the water, they calculated that the bullet traveled 9,000 feet in 18 seconds and fell to earth in 31 seconds for a total time of 49 seconds.

As a comparison, the .30 caliber bullet fired in a vacuum at 2,700 f.p.s. would rise nearly 21.5 miles and require 84 seconds to make the ascent and another 84 seconds to make its descent. It would return with the same velocity that it left the gun. This gives you some idea of what air resistance or drag does to a bullet in flight.

Out of the more than 500 shots fired from the test platform only 4 falling bullets struck the platform and one fell in the boat near the platform. One of the bullets striking the platform left a 1/16 inch deep mark in the soft pine board. The bullet struck base first.

Again, they were interested in terminal velocity more than how high the bullets went, but we can take 2 important things from this;
1. It was a practical test in which a named bullet was fired and an estimated height was obtained (9000 feet in 18 seconds which is about 2743m I think...).
2. It was extremely difficult to get the bullets back to ground within the target area: there was considerable horizontal movement.

There are lots of scary equations here and a calculator which might be useful here but it doesn't give height only time.