Hate to say it man, but that gunsmith saw you coming a mile away... He just got rid of a shitty twist barrel blank he'd never be able to sell, for something he could use. These days people use modern twists like 1:7 to 1:8 for .22 caliber centerfires... He probably ordered that a long time ago for a customer who realized his twist rate order screwup, and never paid him for it, and it's been collecting dust ever since. Then he convinced you it would work fine for what you want, and now he's gotten rid of a blank he'd never be able to sell to a customer in 2024.
Unless you ONLY ever want to shoot light bullets, in which case 65's or less and you'd be ok at good velocities for coyotes.