After loading the pellet, did you happen to load another? Clear the barrel and dry fire it to see if it does the same thing again. It sounds like you blew an o ring. It could be the breach o ring (were you harsh with a cleaning rod and metal brush cleaning the barrel?) or possibly the transfer port o ring if the gun wasn't assembled correctly.
JK's Airgun Forums, moderators, and administrators are not responsible for any problems that may occur from reading or using content posted on this forum, as they are the exclusive responsibility of two parties: the person who posted it and the person who acted on said posted information.Use of our forums from people under 18 years old, only with legal guardian(s) present.