A couple of thoughts from my little experience. The F-15 has on-board systems that allow it to ID the target at beyond visual ranges for ROE purposes.
Most fighter pilots have had very little time actually firing the gun on their aircraft in an air-to-air employment. The HUD display may or not may not truly represent the bullet path. Hitting a high-performance fighter with a gun is more difficult than most believe.
The new newest IR missiles such as the Russian R73M are highly maneuverable, can be launched very far off boresight, and are resistant to decoys.
Make sure your fighter has a helmet-mounted site/display for that visual fight to take advantage of your IR missile.