Are you viewing the bullets from the side or looking at your target like you are actually holding the gun. This will determine where you put your emitter.
Using Particular, use a point emitter, change it to directional, change the spread to 0 to line up the direction toward your target by rotating the emitter in the x,y,and z axis. Then, simply change the spread angle until the rounds spread out enough to your taste. You can mess with velocity and even have the rounds die when they hit your layer if you change the settings to bounce and use your target layer as a wall or floor.
Best of luck
Mike Park