.22 caliber Percussion Muzzle Loader question

[jimhallam]

Wouldn't that be a relatively simple retrofit using barrel liners and breech plugs ?

No -- because BATF&E have determined that such a design would be "readily convertible". That's why the NAA .22ML revolver frame is longer than the cartridge version, so that a regular cylinder cannot just drop in. To be fair, that makes a lot of sense, because cartridge conversions threaten the whole concept of modern-made Muzzle Loaders NOT being "firearms" under Federal Law. There are those who try to blur the boundaries (mainly for financial reasons) but it does the rest of our community no credit. That's why we are now seeing certain jurisdictions overlaying Federal Law with more restrictive ordinances. It has already happened in other countries -- worse in Australia than the UK -- and getting worse elsewhere when the "woke" brigade get control.