A galleon with a mercury and 2 heavy flaks on the left broadside could potentially snipe a ship down before they knew what was going on. Mercury empties the 2 shots from the normal clip, reloads into Lochnagar, breaks the armor, double Lochnagar heavy flak should destroy the hull of most ships after that. Would be an interesting sniping platform. Flame-throwers are useless with experimental rounds as you only get one shot and flamethrower damage is rather pitiful. Mine-launchers only have a single shot per clip, but they reload so fast that the Lochnagar wouldn't be worth it. I have tested experimental rounds with the heavy carronade though and the result was interesting. It didn't seem to have any AOE at all, potentially because of the -50% aoe, just a single, pretty scary hit. On dummy balloon in practice it only took 2 Lochnagar heavy carronade shots to strip the armor off, and seeing as a heavy gun does't get destroyed, this opens doors if you can maneuver the ship to aim at close range. Sadly, the galleon isn't really the king of speed or maneuverability.
I personally view the Lochnagar shot as a utility clip for experienced gunners. Something to reload into when you know it'll make your next shot destroy something before it is repaired. Since you keep your rotation speed until the round finishes loading, the experimental shot can also be aimed in this manner. Could also be used when your gun is on fire to break it right away and fix it up to get rid of flames without losing out on too much damage(unless this was changed at some point, you cant get back into a burning gun once you get out, so this would be useful).