MHP: I Can't Defeat Lao-Shan Lung in the Village Quests

I decided to play Monster Hunter from scratch, so I'm currently playing MHP (Monster Hunter Freedom). I can't defeat Lao-Shan Lung, who seems to be the final village quest (?). I couldn't beat him with a Light Bowgun, and even after upgrading my Hero's Blade to the Master Blade, I still can't defeat him.

Trying to hit his weak spot, the belly, is really tough because my attacks don't land well and keep bouncing off. It's much easier to hit his head, but apparently that only does about half the damage of the belly, so I just can't kill him.

What should I do? Maybe I should save up some money to get that 'Power' something item.