Centerfire versus Muzzle-Loader.
In a fire fight no one can deny that it would be better to have a modern cartridge gun than a muzzle-loading gun, but let’s just look at some pros & cons for something to think about.
Post shtf modern ammunition will no longer be available. Modern ammunition is heavy. You may prefer to carry a 9mm Glock or a 357 magnum, but for most people this will mean having to join a pistol club, paying club fees plus the cost of the handgun & the constant purchase of ammunition, because you have to attend regular shoots to retain your membership & your “H” class licence. If you plan on using this handgun post shtf, then you will need to stock up on ammunition, or at least get as much as restrictions will allow. If you are planning on “Bugging In”, then you can get some reloading equipment. It may not be practical though to carry this reloading equipment with you if you have to leave home. It all depends on how heavy & bulky it is & you do not want to compromise your survival by not carrying enough water, food & ready made ammunition. Don’t forget that if you are planning on reloading your own ammo, you will need primers, possibly more brass, smokeless gunpowder & of course lead.
A flintlock pistol only requires gun flints, gunpowder, wads or wadding & lead. Any siliceous rock will work in a flint lock. Black powder, wads & wadding you can make yourself, & lead is easy to come by & you can mould your own ammunition. You can also make paper cartridges for faster reloading if you have a smoothbore. A smoothbore pistol can fire shot & round ball, either or both together.
You do not need a licence, registration or a permit to purchase in NSW (check your own state legislation) if you are buying an antique. You don’t need to carry a lot of lead, as you will only be using this pistol for defence. If you have the stomach for it you can retrieve spend lead from a dead foe or game & remould it. No heavy reloading equipment is required, just a ball mould & a small lead ladle. Gunpowder is light in comparison to lead, so you can carry enough to last you a very long time. If you were to run out of lead, you can substitute other projectiles obtained from nature.