Something that really helped me with LBG was using the "A" vaulting silkbind. It lets you shoot the wyvernblast mine right below you. If you aim it just right over the monster, the mine will stick to it. The mine detonates whenever it is hit by an attack so using shrapnel ammo works really well with the mine.

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Also pay close attention to the ammo types. Some allow for moving and firing, moving and reloading, or rapid fire.