EdGi have redesigned their SAP piston heads to deliver higher levels of power using lighter springs. 
 
Already own a SAP piston? this SAP piston head is compatible with existing SAP pistons
 
Recent builds for the TAC-41 and SRS are achieveing 2.28j using 0.45's whilst using the Silverback 100Nm Spring (a very light pull)
 
This new piston head still comes with an O-ring but this should only be used on slightly larger diameter cylinders
 
This product is recommended to be used with the Longbow Rifle Lube