S.I.R.

The S.I.R., or Standard Infantry Rifle. The idea for this rifle was not mine, but was the idea of the author of "World
War Z", a book pretty much about zombies taking over the world. In the book, among the weapons designed to fight them is the S.I.R., a rifle specifically created for anti-zombie warfare. It uses interchangable barrels: short carbine, medium rifle, and long range sniper. It is steel and wood construction, unlike the synthetic plastic firearms of today, so it is more durable. It also has a wide ejection port to avoid jamming, as well as a variety of scopes and sights. In the book, because zombies can only be killed by a clean shot to the head, the gun can only fire in semi-automatic mode, so to improve aim.
Ammunition comes in the form of a bullet called the "PIE round", a round that explodes on impact with a target (being the brains of the living dead).
According to what was written, the design was a combination of the new US XM-8 and AK-47 assault rifle.

World War Z is copywrite author Max Brooks.