On our handis with rimless cases this is not so uncommon. But it is generally, NOT a major issue.
Clean the chamber! Before shooting, sure your chamber is clean and DRY, especially, NO OIL!
Try Tims suggestion, take a REALLY good look at the brass that came out of that chamber.
I have found that too much OIL in the chamber is likely the trouble.
GOOD LUCK!!
CW