".50"
Foreign Countries have a problem with yachties bringing arms into a port. If you delcare your weapons chances are better that they'll be confiscated and you'll probably not get them back.
If you don't declare them and they are found on your vessel, smuggling charges could be brought and you'd be spending time in with 3rd world buddies behind bars, most likely losing your boat in the process.
From what I've read in cruising news stories a shotgun is the maximum firepower a number of countries will allow you to posses in port, and it will be locked up in the harbor master's office for your duration of stay.
How about a flare gun? Would that be suitable for close quarter battle? I've never fired one, so I'm not sure if they're acurate enough to deliver a pyro technic on target.
That's what I have read as well, and with slugs it will penetrate the hull of anything under 50 feet long except possibly a heavy duty metal work boat. Good slugs will also shoot maximum 4 inch groups at 150 yards. If you start shooting beyond that range you are likely to be considered the pirate.
SO9