.22 burst cases

Hi everybody, I've made multiple very nice 3D2A builds so far, but only with .22's I get an issue I can't solve on my own.

After nearly every shot, the case ruptures and gets stuck in the chamber, I have to pull it out with tweezers. I've got this issue on multiple completely different .22 builds, all using a 8mm OD x 6mm ID liner. So far on the NULL-22 and on both of my HD22c.

Ju5t3nc4s3 wrote on the sea, that the chamber needs to be tampered and polished. But what is he meaning? Can someone explain further? How to tamper a 6mm ID tube? If I would try to polish it, I would get 6.1...6.2mm in the end. I'm confused.