Mega Shell with 3 different sets of ID. Based off of the Mega Caliburn barrel ID (19.74mm), a tek6 plunger tube ID (19.05mm), and hopefully a nice middle ground (19.30mm).

All my shells require an upgraded seal. Everyone's seal is different and you may need to adjust only the height to make sure the interface with the seal is perfect. Modification of the ejector and cutting of some plastic bits is required.