I have tried to install different manufacturers collapsible stocks on my flex stock buffer tube. I tried a Rogers superstoc, and a FAB defense GL stock. Neither were even close to fitting. It appears that the buffer(nylon?) installed by Mossberg is not compatible with other manufacturers stocks. I asked Mossberg and was given the standard CYA: "The Mossberg FLEX system is designed to work with Mossberg components." and "We would not recommend changing the buffer tube because any failures could void the waranty." Has anyone else experienced this issue? Has anyone changed out the Mossberg buffer tube? Thanks. Dan