I have put around 1000 25.4gr JSB pellets through my .25 GK1. The power is set to 700 ft/sec. I started to get doubling occasionally. When it happens, it is very fast. It sounds like one long noise. I have no idea what is causing it. It appears that the secondary sear is not catching, but I'm not sure. yet. Has anyone else experienced this? I also experienced my first magazine jam, where one pellet fell into the barrel when indexing. To clear it, I simply took a .22 cleaning rod and tapped the pellet back into the mag. No issue.