Perhaps the butane feels richer because it has more space and therefore the illusion of more freedom within the closed domain after the propane is gone. Perception is reality.
Measuring bottle pressure. You can do this as a permanent or temporary addition to your regulator. Most if not all the small regulators have 1/4 inch pipe connections. remove the Propane tank connector from the inlet side, add a 1/4 inch pipe Tee and a close nipple, then a gauge. This 100 psi gauge is only good to about 65 degrees, before it pegs out. note the pressure is 83 psi at 50 degrees on my tank. That's what it should read for 100% propane and it does.If you google propane vapor pressure it should be 78 psig at sea level and 50 degrees. At my altitude (7300 feet) it will be 4 to 5 psi higher and it is. In your case you may just want to refill at a different place and see what happens. With an outside thermometer like this you need to make the measurement before using the forge or the pressure will be too low. Not sure of the problem, but wasn't able to upload a picture.
Jack I think it is the amount of methane and ethane C1 C2 that are making the propane freeze up. If the operator is not watching his fractionator temps while making propane he or she can ruin a whole load. Most propane is considered acceptable at 85% C3.
