Yes.  I was bored and bought a POS ATI 16" .450 upper.  BCG included.  Runs fine hand cycling but fails to eject when firing.  It DOES lock the bolt back on the last round.  But it leaves a semi-mangled piece of brass in the ejection port.  I have tried a couple different buffer/spring combos and while it seems the lighter ones mangle the brass less, it still won't eject properly.  I have checked the ejector with the BCG out of the gun and it seems smooth, but it also looks like the extractor feels a little "sticky" while testing.  It's like the ejector can't get the brass out soon enough and it's jamming the case mouth into the front of the port.  Overgassed?  IDK.  It really does seem to be pretty damned accurate so I would love to get it to run.  Using C products mags BTW.  Does it on both 5 and 7 rounders.
Have tried Hornady American Whitetail and 250 gr FTX so far.

Sorry meant to post this in the "AR Variants".  Mods please move.

Does it have a standard milspec upper with normal ejection port, or has is the port opened up wider to allow better passage of the thicker brass?  That was a common problem for builders using a milspec style upper that was remedied by hogging out the port.

Looks standard to me...
Thanks for the clue.

That pic above I found on the net, but when I built by BM upper, I used a cheap milspec upper and opened it up myself like that image with some files and a dremel with grinding wheel, then hit it with aluminum black after.  It worked great for me.

Good pic!  I used a standard upper and milled out the front of the port just like that.  

Bolts are a sticking point for the 450 BM.  Some just flat suck at feeding and chambering but it seems yours is doing that part okay.  I would replace the extractor to begin with as that seems to be the main culprit.  I had a 1911 that wouldn't eject for shit and then someone suggested the extractor so I bought a good one and it has run 100% since.  If the hook isn't getting a solid purchase on the case head it isn't going to pull it out with any consistency.

A heavier buffer should slow down the cycling, but it appears you have played with that already.  Spring shouldn't matter on ejection cycle, but you never know until you know.