Cleaning a GM drop in barrel today and saw this. It looks like a stainless steel helicoil in the nipple threads. The crossways piece in the bottom seems to be from the helicoil having turned itself in beyond the threads that hold it. I've had this barrel for a long time now and today was the first time this appeared. It's not something I previously overlooked. It's too obvious when you go to reinstall the nipple. I have heard of helicoil problems in the past with GM barrels but I thought they were used on the breech plug threads. What do you all think?