I have another reply to this thread, with regards to the barrels.
I was told by Len, when I purchased my L4, that the barrels were actually 1919 Israeli barrels, that he somehow fits inside the original parts or exterior of an L4 barrel!!? Makes it sound good, as there are many new, surplus Israeli 1919 barrels available...sometime, Len will dazzle with tales of fascination and my mind wanders. Hence not recalling every detailed word he used to describe the process.
But does that make sense? Is it possible?
There are obviously STILL set up issues with HA guns, and that is becoming more and more clear as time goes by. I recall my first HA purchase a number of years back. Never could get the problems resolved and Len had it twice for R&R. In the end, they gave me a refund.
It is troubling to me that he seems to be building "models" of guns and not so much, actual operating guns. I know I am being a bit harsh, but he sells them as FIREARMS...they should run.
BTW, NOBODY is going to like this solution, but I found, with HA MkI, that it WILL reliably run PPU and Wolff .303 if I spray oil the cartridges first. Not a great solution, but allows me to save the military grade ammo, that does run reliably in the .303 (MEN & Britishmil spec). A different story for a different day. I have not had case separation issues with the HA MkI, unless running PPU or Wolff.
My L4 problems boiled down to too much spring pressure, inducing short stroking and jammed cartridges on feeding. That was resolved by clipping two coils from the striker spring! Thank you MilSurps Expert! Gun runs well on gas setting 3. My L4 has NOT had any case separation issues like my .303. So your issue, may not directly correspond to my issues? Different gun, different caliber??
I would say, if you chamber looks rough, I would have a tendency to want to polish in a longitudinal fashion, instead of the rotary method. Just slowly and minimally. Try to remove less metal, plus, the case is extracting along that bore axis. But I suspect you have done what polishing you were thinking about, so a late point. Not sure what tool to recommend for that? Additional or new L4 barrels are not easy to find. Hopefully, someone might do a run in the future??