The Speaker
Brian Turner appears to be this poem's speaker. He's experiencing inner conflict regarding the difficulties of war he faced as a soldier. The speaker comes to the realization of his body's vulnerability, which is exploited through war. This moves him to figuratively sacrifice his body (or someone else's) up to the bullet, a symbol of war and personified enemy of the speaker. He describes the bullet damaging the body in a variety of ways. Yet this isn't enough to damage the spirit and courage of the speaker.
The Bullet (Personified)
The bullet is the personification of war's atrocities against human nature as well as death's power. The speaker describes the bullet attacking the human body and weakening its defense mechanisms. It's as if the bullet's attack on the flesh is merely symbolic of the attack on integrity and dignity the speaker possesses. On the other hand, the bullet is overpowered by the speaker toward the end of this poem.
