So from my knowledge to shorten it and condense it. If it is a modern reproduction and used Flint,wheel, or match lock sky's the limit as long as it's based on a "historical" firearm they don't really define the "historical part". Technically you can't "legally" produce a percussion muzzle loader as it is now necessary to have a manufacturing licence to produce non restricted firearms, a percussion ignition firearm is considered modern if produced today no matter the style. Now don't be discouraged if it is a time period piece it is okay for import as a antique if percussion looking for large calibre/gauge guns or rifles look to Europe at auctions the NA market has to little supply to the demand while in EU it is relatively flipped, that's what I did for my big bore guns and rifles.