from the wiki:
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If the blowpipe is not protected upon death, all scale and dart charges will appear on the floor alongside the blowpipe. If the blowpipe IS protected upon death, ALL scale and dart charges will be maintained when you respawn. This makes it an effective weapon for ranging in the wilderness as the weapon and the ammo is contained in one high-value item slot, being very effective at Revenant Caves for those who are not skulled.