In spite of popular belief, the flat BB BP is not a prime pec/chest builder for most people. Also try not to be swept away with that 400lb number, or any other number, when it comes to building muscle mass. Those 400lb + benches (in reality, some of those weights listed fall more into the 330-350 class) that you read about the Pro's and other men using, are usually between a quarter to three quarter range, very fast reps. Rare are the full ROM movements of these huge guy's.
You could develop an exceptional chest/pecs with weighted dips (V bar dips are useful for wide to narrow hand gripping...different angle & stretch), DB flat/incline presses, pec deck, cables, etc. Can also consider BB benches to the neck (wider hand spacing places more action on the pecs). Though this exercise is not for everyone. Might use caution and go light on this one at first. Good Luck.