Short answers, pulled from the story.
The first rifled gun barrel appeared in 1440. Military commanders refused to use them on the battlefield for three centuries due to the difficulty of loading. Early rifles could fire perhaps one shot every three minutes compared to three shots from a smoothbore musket.
French Army Captain Claude-Étienne Minié invented the Minié ball in the 1840s. This conical bullet featured a hollow skirt that expanded upon firing to grip the rifling grooves. The innovation solved the century-old problem of loading speed and transformed the American Civil War.
The German Dreyse Needle gun was the first breech-loading rifle to see significant use when it was introduced in 1836. It was followed by the French Tabatière in 1857 and the British Snider-Enfield in 1864. These mechanisms allowed for a rate of fire many times faster than their muzzle-loading predecessors.
The record for the longest confirmed kill shot stands at 2,430 meters. An unnamed soldier with Canada's elite special operations unit Joint Task Force 2 set this record using a McMillan TAC-50 sniper rifle. The bullet rotational speed can exceed 270,000 revolutions per minute to ensure stability at these extreme ranges.
The Grizzly, a 3D-printed .22-caliber rifle, was created around August 2013 by a Canadian known only as Matthew. The original Grizzly fired a single shot before breaking, but the Grizzly 2.0 managed to fire fourteen bullets before suffering damage from the strain.