I've sleeved chambers before (including a Type 99 LMG to 7,62x39 for a fellow), but never considered using a barely press fit sleeve as the way to join assemblies like this. Mostly because as soon as high pressure gases enter the front join face, it would begin to act like a piston to drive the assembly apart. It's one thing to have a sleeve come loose on a one piece barrel, but this idea....very bad indeed. I've looked at a number of these rifles over the years, but never even had any inclination to think it was put together in such a way. Nor remember being mentioned in any of the various reference books, dating back to WHB Smith and Melvin Johnson. You'd think Johnson, as a firearms designer himself, would notice such a thing!