My catch bucket method involved directing the shot stream into a cheap plastic funnel which had a rubber tube attached - flexible enough to feed the shot into a cheap plastic bucket. A hole was made in a piece of very fine gauge netting (finer than the shot size). The rubber tube was then fed through the hole in the netting and an elastic band used to secure the piece of netting to the rubber tube. The netting was then spread over the top of the bucket and secured with a piece of elastic string. Netting over the bucket prevented shot escape and also prevented build-up of air pressure. The bucket was placed such that the rubber tube went through a gentle curve of about ninety degrees.
Total cost was the equivalent of two US dollars - within my University's petty cash budget!
With regard to your second question: you could reduce the air pressure on the one nozzle until it read the same as when all eight nozzles were in use.
