Knight Mountaineer .50 cal. I did notice on the 4th bullet I loaded there was a spec of plastic left from the sabot. It shoots them really well, but they are just a pain to load. I'll switch over to the .452's over the summer. I have it dialed in now with the 275s I can deal with it for now. I also noticed the 275s fly right with the 200 grain tc shockwaves, maybe I'll use those for now.