I heard that the BBs will begin to swell and cause guns to jam if theyve been exposed to moisture for a long period of time?
This is not true with Excel Bio-degradable BBs. In the past, some Biodegradable BBs made by Marui were made from corn. These BBs degraded in only in one month time. The only drawback was that it was sensitive to moisture. When exposed, it would swell and cause airguns to jam. Excel will not expand when they start their degrading process. They just dissolve.