Do you need the 16d's? Is that what's called out on the specs from the engineer? You can get by with 10d's in general, but make sure from the plans/specs first. Next question is are you using the nails from Simpson? They are more resistant to bending.
One of the nail guns made specifically for this usually gets it close. You may have to sink half of them the rest of the way. Nailing Paralams are fun, aren't they?