"when the A/C blows on them"
Man either them're some light cars or one heavy duty blower all right!
When I was a kid, I remember laughing hysterically when my dad huffed and puffed and blew an AHM Pullman completely off the track. I was complaining that it was derailing - while mixed in with some old Walthers wood & metal cars when he made the observation "Well no wonder - this Pullman is so light I can blow it over", which he then did.
Years later I had complete trains of AHM passenger cars. I found that goo-ing the worthless couplers together, as well as adding some sand bags, made them almost usable.
I always wondered if the Rivarossi/AHM stuff was ultralight (the only metal in the passenger cars were the axle tips and coupler springs) just to save on the shipping from Europe.
I recently did some weight comparisons between various passenger cars of various vintages. I had an old undec (paint adds a few milligrams
Rivarossi 12-1 Pullman. It managed to be the lightest of the entire sampling - and that was weighing it *in* the box.
Heaviest passenger cars I own are OMI/Ajin Santa Fe high-level cars. IIRC they tip in at about a pound each. I also have some E&B Valley cars I built up; one coach has lead slab floor weight (linotype actually) and then has metal seats. I think it's 12.5 ounces.
IMO most passenger car models are a smidge underweight. Walthers cars track visibly better just by the addition of their lighting unit. I don't really have a standard weight, but I'm guessing my best fleet passenger cars are about 50% over NMRA standards.
Andy