Is there a scale in your gym?
Me and another guy weighed one just recently, and it was 17.5 lbs. The number seemed a little odd ( I 'spose it was... ), but we weighed it 2 ways, by itself, with just a fingertip balancing it, and with him on the scale with and without the bar, and subtracted. Both ways came out the same.
They may not all weigh the same though.