It's probably your form. On BB Bench, be mindful of the following:
- Arch your lower back up slightly so you can fit your hand between the bench and your back
- Pin your shoulders back, as if you're trying to hold a pencil between your shoulder blades
- Whilst pressing, consciously squeeze your chest in as you lift. This essentially means squeezing your elbows in together as you press
- When returning the bar to your chest, keep it slow and controlled - the negative is also important on a pressing movement.
Really focussing on squeezing your pecs will result in hitting them much harder in my experience. There's no reason why your chest should feel un-worked during flat benching.
