In addition to precise weights, other factors add up when you get to the railway gun class. The Paris Gun had projectiles graded by size to be fired in sequence. Erosion of the bore was predictable and each shell was incrementally larger.

Coriolis force was another thing to factor in unless you were shooting due east or due west.

That's a row of projectiles on the ground next to the gun carriage. Each one has its exact weight in pounds chalked on its bottom/base: "1069", 1070", "1071" etc. Even seemingly insignificant weight differences of a pound or two had to be factored into the complex mathematics involved in aiming large caliber artillery like this.

What does the "35-caliber" designate?

[In artillery, caliber can be either "the internal diameter of the gun barrel or a relative measure of barrel length" (in this case, 35x12 inches). - Dave]