You need something thin and strong, I'm not sure delrin would work. There is an initial burst of pressure as you pierce the 12 gram, and a pressure when the gun is fired, which will collapse weak materials.
I also think that it is worth looking into improving the flow into the cupseal, possibly by porting around it at the top of the insert opposite of the pierce pin. There is very little room left between the cupseal and insert as it is, which may hurt efficiency.
Originally Posted by agentSmith
oldschool play is about sportsmanship and respect, oldschool gear is available on Ebay.