what caliber do they shoot in biathlon

In modern Olympic and World Cup biathlon, athletes shoot .22 Long Rifle (.22 LR), a small‑bore rimfire .22‑caliber cartridge.

They used larger full‑bore calibers (like 6.5×55 mm and similar) decades ago, but since the late 1970s the rules have standardized on .22 LR for international biathlon competitions.