FMJ

A full metal jacket, or FMJ, is by far the most common bullet type. Common design has a copper jacket encasing a large lead core. This bullet type deforms depending on point of impact and obstructions, rather than expanding ("mushrooming").

This and its fair performance against both flesh and armor make it a popular choice with gunslingers. They never suffer penalties, but don't get the damage bonus of JHP ammo, or the armor-punching power of AP ammo.

Fallout Tactics
There are no types of FMJ ammo in Fallout Tactics. The .44 Magnum variant has been replaced by .44 Magnum ball, and .223 weapons were changed to accept 7.62mm.