I swapped the barrel lugs from my other barrels, same thing, all other barrels lock up tight. The lugs from this barrel on my others they lock up tight. The hinge pin fits VERY snug in this barrel with just a small amount of play in the frame. My other barrels have a little play in the hinge pin hole but they still lockup tight. It makes no sence. I am going to try a stronger lug spring from Mike Belm and see if it makes any difference. I also have a larger hinge pin coming but I'm sure it won't fit the barrel and I don't want to ream it.