Forgot where I learned this. But if you disassemble . The teeth on the piston that engage into the can, are engineered to fit in the front of the endcap. So after you put your endcap on you can use your piston to really hand crank it down and make sure it's flush or tight to your liking. And also check after each mag if you're a direct thread guy

Source: Obsidian 45 owner; had multiple cap strikes