The AM-40's name means "Ascension Marine .40 Cal". It is a semi-automatic sniper rifle used by the Imperasins with a heavy kick to it, yet at the same time is light. With a heavy kick on the butt end means a heavy kick on the bullet's end, and so when this is fired and finds its' prey, they would better hope it hit their head.
The AM-40 has a fairly large, titanium barrel with rail mounts going half-way from the body on either side. The body and stock are made of solid steel, yet the butt has a rubber cushion on the end. The pistol grip is interchangable and iron sights lay atop the gun. A large banana magazine is used to hold the .40 cal bullets. A flash hider is built into it.