Look at the shell casings that you've already shot. Look for scratches that run the length of the casing. If there are scratches, the chamber may have debris/machining roughness in it. I had the same problem with another brand .22 WMR bolt action pistol. I used a chamber brush and just kept turning it over and over again. It doesn't take much resistance to pull the spent casing out of the grip of the extractor. If you don't have any spent cartridges and go to the range, polish 2 or 3 casings so you can see the scratches better.