For a month at a time he would shoot six to eight hours a day, filming the sessions for verification. His latest monthlong attempt, beginning May 8, was his fourth.

The tally sheet for his effort shows a load of 112s and 171s and 289s, with an occasional score over 400. On May 15, he set a personal best of 490, still 36 short of Mosconi. “That was the best I’ve ever done,” he said. “But it was incredibly frustrating.”

Finally, on Monday, he opened with a 126, then recorded his big 626. “When I got close to 500, I was conscious of the chance of ‘dogging it,’ what we call choking,” he said.

Mike Panozzo, the publisher of Billiards Digest, praised Schmidt’s “focus and the perseverance to run 380, and then you miss and start over again.”

Mosconi was one of the greatest to play the game.

“There will never be another one like him,” said his wife, Flora, at the time of his death in 1993. “He reminded me of a ballet dancer going around the table. He was so quick, so smooth.” His rival over the years was Minnesota Fats, perhaps the only pool player with more name recognition, even today.

Mosconi’s 526 happened under circumstances somewhat different from those that Schmidt faced on Monday. Mosconi, then 40, was playing in an exhibition match with a man named Earl Bruney in Springfield, Ohio. After defeating Bruney, he just kept shooting until he reached 526. In contrast, Schmidt was purely playing for the record, with no opponent, starting anew each time he fell short.