101Leafy researched the games.
Mythical Three-Horn

Crafted from notes found at the old Tower and outfitted with Rapid Fire Clust S Lv1.
A weapon made by hollowing out three Kirin horns as barrels and binding them together with its mane. It is a bowgun revived from a method written in an ancient document unearthed at the Tower, and it even has rapid fire for Clust S, which present-day techniques simply cannot make.
Our translation of 復刻 ハンター大全 (KADOKAWA / Enterbrain, 2014), page 168.
| Class | Light Bowgun |
|---|---|
| Rarity | 10 |
| Attack | 336 |
| Slots | 0 |
| Reload | Average |
| Recoil | Medium |
| Rapid Fire | Clust S Lv1 ×2 (60% power per shot, very long recovery) |
| Table price | 8,000z |
Ammo
From モンスターハンターポータブル 2nd G 公式ガイドブック (Enterbrain, 2008), page 776.
Materials
SpecialKirinHide ×3, Platinum Mane ×4, Kirin Azure Horn ×3, Purecrystal ×2