fail to eject issues

[hatidua]

Those (many) of you whom are far smarter and more experienced than I, can hopefully weigh in on this:

The first order of business when I arrived at the range this morning was to dial in the iron sights on a 16" carbine-length upper. The first 15 or so rounds all functioned fine. Then, I pulled the trigger and there was nothing but a 'click' - which was odd as I knew I still had half a magazine full to go before I was empty. I pulled back the charging handle and there looking at me was a live round happily sticking out of the end of the bolt. I released the charging handle, pulled the trigger, yet another 'click'. I went to pull the charging handle back again but now it was stuck rather well and I could not pull back the charging handle. I mortar'd the rifle stock on the bench and free'd the round from the chamber but it was still very happily married to the bolt. I pulled the charging handle back and let it go one final time, this time instead of the dreaded 'click', it fired. However, the round still would not eject.

The upper is used (BCM M4 profile 16" upper), probably has 2K rounds through it (not by me, I recently bought it used - had I not been told the upper was used it could easily pass for brand new). The BCG (BCM) is brand new, it has seen a total of 16 rounds since new.

So, what might be the problem/s? -yes, I'll get the rifle in front of a gunsmith but figured I'd post this in the meantime to see what people think...