eightbore,
As far as I know, the full length, full caliber Einstecklaufs that adjust at the muzzle(V.V.V.)were developed by Hans Zimmermann in the late 1970s/early 80s and he started marketing them in 81-82.Since then, a couple other makers have come onto the market. Sleeving is likely more than a hundred years old, but it usually used soft solder, rather than threads.These barrels were adjusted(regulated)the tradional way.
Mike