Bill, You might attempt testing the air flow in both tubing styles.
Use the one with the lowest parasite drag (air resistance on the
internal walls).  Most likely the brass will have the least resistance.
A HVAC anemometer is the tool I use.  I suggest reaming or cleaning the
internal walls also.

Ray Bauer
Lake Tahoe, California

 [ HVAC = heating, ventilation, and air conditioning.  See, e.g.,
 [ http://www.professionalequipment.com/anemometer/  -- Robbie