All my muzzleloaders are mostly British military pattern guns. A mix of flint and percussion, smooth bore and rifled, original and reproduction. A friend who is a world class shot lent me a couple of books. Those Limeys had a pretty good handle on what works almost 200 years ago. An Enfield P-58 Naval rifle is amazingly accurate. But my doomsday, TEOWAWKI, would be a Northwest Trade musket, or the next best thing, a Brown Bess. They can outlaw primers but they can't outlaw rocks. Two hundred pounds of Kentucky cave dirt will still yield a pound of saltpetre. While limited by range, a smoothbore musket has the flexibility to kill anything that walks crawls or flies pretty efficiently.
Hand-book for Hythe: Comprising a Familiar Explanation of the Law of Projectiles, and an Introd. to the System of Musketry
Rifle ammunition, notes on the manufactures connected therewith, as conducted in the Royal arsenal, Woolwich