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Micro-groove will not shoot cast bullets. That is purely a myth. As with any barrel the cast bullet must fit or it will not shoot well. Micro-groove is a button rifling process and will make the groove dia. slightly larger than a cut rifle barrel. That means that a MC barrel will usually require a cast bullet .001 or so larger the a Ballard or cut rifling barrel.
Jacketed bullets seldom require an accurate fit to shoot well but the cast bullet needs a perfect fit to shoot it's best otherwise the powder flame can escape past the bullet as it moves down the barrel. The flame cutting of the bullet will destroy accuracy.
My rifles like a LaserCast 405 bevel base bullet over 13 grains of Unique at about 1300 fps. No filler. That closely matches the original Black Powder loading. It is also a killer on any game animal in North America. And, it doesn't kick the snot out of the shooter.
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