What is the difference between a SCUBA tank and an SCBA tank for filling?

A SCUBA tank is rated to roughly 3,000 PSI, holds breathable air, and is filled at dive shops.

An SCBA (Self-Contained Breathing Apparatus, used by firefighters) tank is typically rated to 4,500 PSI in carbon-fiber wrap, much lighter, and holds more usable air for high-pressure airguns. SCBA tanks dominate the airgun world because most modern PCPs run at 250 to 300 bar. Both require periodic hydrostatic testing - usually every 5 years for steel/aluminum and 3 to 5 years for carbon fiber, with a 15-year service life on carbon.