The white plastic part you found is a hammer debounce device that stops the hammer from striking the valve stem after the shot and waisting air. I think there is more of this small part that you have not removed. A drop of lube was needed on this part every hundred shots to keep it working properly. I have one in my .22 Disco along with a air control unit installed so I get 80+ shots from every refill at about 620 fps. Look up Airguns of Arizona and check custom Disco parts to see these parts.
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