This is a very poor test to gauge a lens's sharpness.

Shots 1 and 3 show a shutter speed of 1/350 and 1/250 respectively. These speeds are too slow for use on a 300 mm lens trying to track a moving target and reveal zero information about the sharpness of this lens. IF your focus was bang on (which is VERY hard) and you shot at 1/1000, then maybe we could attribute this lack of sharpness to the lens, maybe.

The rule of thumb is 1/focal length of the lens so shot 2 is too slow even for a stationary subject let alone something as fast as a bird.

Slap the lens on a tripod and shoot some text on a newspaper pasted to your wall at different apertures. Use a cable release. NOW you can gauge sharpness. Hope that helps - Marko