All the shotguns you see here evolved from the less reliable and less effective guns of an earlier period to the reliably accurate and artistic designs of modern firearms. All it took was a little-known gunsmith with some knowledge and patience to change the shotgun forever.

Choke boring, the constriction of the shotgun bore near the muzzle, was the most significant technological advance in developing shotguns. Shotgun bores without this constriction produce inconsistent distributions of shot in the pattern. From the beginning, shotgun makers sought methods of delivering consistent, more efficient patterns in their guns. Most relied on making large bore guns capable of shooting heavier charges of large shot, but the problem remained unsolved. One maker, Roper, attached a sleeve with a reduced bore to the muzzle of his guns. This improved the pattern; however, the Roper mechanism was faulty.

Fred Kimble, an ardent waterfowl hunter living along the Illinois River after the Civil War, desired a more efficient shotgun. With few tools and scant mechanical expertise, Kimble began experimenting with a muzzleloading musket. Disassembling the musket and removing the breech plug, Kimble began the laborious task of enlarging the bore from the breech to a short distance behind the muzzle. Then, using a hand-cranked homemade reamer, Fred went to work. With a hand-powered reamer, the better part of a day may be spent making one pass up the bore to the stopping point; then, the gun would be reassembled and shot. Preliminary results encouraged Kimble. He continued enlarging the bore until disaster struck – the gun threw more horrible patterns than before it was enlarged.

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Source: https://traphof.org/inductees/details/1/84-kimble-fred​

Patience somewhat abated, the frustrated Kimble decided to remove all the constriction at the muzzle. Not happy with the prospects of disassembling the gun, he began reaming the constriction beginning at the muzzle. Without proper measuring tools, he thought all the constricting was removed. Loading and shooting the gun, Kimble found the entire charge within a 30-inch circle at the test distance, about 40 yards. Repeat shots gave like results. Disassembling the gun, Kimble found a small amount of constriction remaining in the bore at the muzzle. By accident, a backwoodsman and shade tree mechanic discovered choke boring. Shotguns and shotgun sports were forever changed. See these types of shotguns and others within our weapons museum today.

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Source: https://www.boxallandedmiston.co.uk/shotgun-anatomy/shotgun-chokes-explained