Pilum

This tip of this heavy javelin is designed to break off and embed itself into a shield once it reaches its target.

Source: Pathfinder d20pfsrd.com

Benefit: Like ammunition, a thrown pilum that hits its target is destroyed. If you hit an shield-using opponent with a pilum, he loses the AC bonus from that shield until he takes a standard action to pry out the remnants of the pilum.

Ranged Weapons (Martial)
Martial Weapons	Cost	Damage (S)	Damage (M)	Critical	Range Increment	Weight	Type	Special
Pilum	5 gp	1d6	1d8	x2	20 ft.	4 lbs.	P	see text

Source Advanced Player’s Guide