Jacketed hollow point

Characteristics
A jacketed hollow point bullet, also known as JHP, is designed to cause severe damage by expanding on impact with its target, while minimizing the distance it penetrates. They were designed in an attempt to reduce collateral damage, as their penetration is impaired by the function of the hollow cavity. The bullet's nose, rather than being pointed, is recessed, or hollowed out, hence the term hollow point. The lead cores in jacketed hollow point ammunition is coated with a harder metal known as the "Jacket" or "Plate". This is to increase bullet strength and in an effort to protect the barrel of the gun from lead residue, cast-off, and striping. When a JHP bullet strikes tissue, or any other surface, the lead around the hollow cavity is forced outward, causing the bullet to "mushroom" and fragment, increasing its diameter and resulting in a larger and wider wound channel. However, the hollow cavity makes for very poor penetration, as the hollow cavity will cause the bullet to flatten prematurely upon hitting a hardened target, causing minimal penetration.

In Relation to the Game
In Fallout, Fallout 2, and Fallout Tactics, JHP bullets do more damage to a target than a FMJ round, but have less armor penetration. This means that, although you may initially hit a target for a large amount of damage, the target's armor negate a great deal of damage, if not all of it.

Inconsistency over effectiveness
While JHP rounds are ineffective against armored targets, armor piercing, or AP rounds are ineffective against fleshy targets. This is best observed while fighting the guards carrying the K-112 assault rifle from Vault 15 in Fallout 2. They initially loaded with 5mm JHP and deal about 22 points of damage in a mid-ranged burst against characters wearing combat armor. However, the guards carry only 5mm AP to reload with. Subsequent bursts from the same distance often fail to deal any damage at all.