It MAY be a muzzle loader, certainly doesn't appear to have a way to breech load it obvious. But, if you think this is an old timey "pirate" cannon firing round balls, you're not looking closely enough.
Watch the shot as it flies, it WOBBLES. Its not a round ball, its oblong and most likely a scavenged artillery projectile, possibly modified.
There are two different gun barrels being shown, the one at the beginning is different from the one shown 30 seconds in...and the breeches are different.
Nor is it shooting black powder. Its something else being used, something that doesn't smoke as much as actual black powder.
Its an improvised bomb thrower, and we don't have any way of knowing if the gun being fired is actually the one hitting the building and doing the damage.
The second gun looks like an original cannon breech with trunions was used with a "subcaliber" tube inserted, using the old trunnions as part of the gun mount. Also note it is being "fired" by someone well off camera using a long lanyard.
Its possible the thing is bits of real images photoshopped/edited/CGI to make it appear to be something its not.
of course, some folks will believe its real, after all, they saw it on the Internet!
