bench barbell dumb bell

[Linuxian]

I'm no expert but I bet you hold the BB too far up on the chest. If the bar rests up towards the clavicle head of the pec as it comes down on your chest, it forces the Delts to do more of the work. The next time you use DBs, compare where the DB's come to rest in comparison with the bar. I'll bet the DB's come to rest farther down the pec.

[BBall6]

I'm no expert but I bet you hold the BB too far up on the chest. If the bar rests up towards the clavicle head of the pec as it comes down on your chest, it forces the Delts to do more of the work. The next time you use DBs, compare where the DB's come to rest in comparison with the bar. I'll bet the DB's come to rest farther down the pec.

Either that or he isn't coming down as far with the DB's. Another possibility is how far apart his hands are on the bar.

When doing DB the hands usually stay closer together than on BB bench.

If Linuxians suggestion and the depth of the lift are the issue, try experimenting a little on hand position and see if it makes a difference.