HK 556 extractor issue?

[BizBuilder]

I just received a HK 556 I purchased and took it to the range for the first time. I had maybe 30 rounds through it and it jammed. I had the range officer clear it and he took out the pictured round. Am un-fired round is jammed into the top half of the case of the previous round. I found the case bottom (pictured) on the floor.

What causes this??