Complex sentence: Single-stroke and multi-stroke guns utilize an on-board pump to pressurize air in an internal reservoir, while pre-charged pneumatic guns' reservoirs are filled using either a high-pressure hand pump or by decanting air from a diving cylinder.
Split into simpler sentences: Single-stroke and multi-stroke guns utilize an on-board pump to pressurize air in an internal reservoir. Pre-charged pneumatic guns' reservoirs are filled using either a high-pressure hand pump or by decanting air from a diving cylinder.