Not quite sure what that means, but my Greener has been sleeved with .577 rifle barrels in the traditional sense, meaning the shotgun barrels were lopped ahead of the flats, reamed out, and maybe threaded (not sure). The .577 barrels had a ferrule turned on the breech end (and maybe threaded) to fit into the 'monobloc'.

Personally I don't really mind whether they were threaded or simply tinned into the monobloc, the gun was proved so all is well. I could always phone Rolph B_ and ask him, if I ever start to lose sleep over it!

The strikers are not bushed, however the Greener has relatively fine firing-pins so the risk is small. It would be better had it been bushed of course, but no worries so far. I have witnessed an FN shotgun pierce a primer, and the blow-back through the firing-pin hole blew the side of the stock-head off. The errant chunk of walnut landed about 30 yds away! A friend has a .400 NE A&N double that has suffered the same fate at some point in its past, the sliver simply reattached with epoxy-resin awaiting the inevitable restock.

BTW bonanza, the chamber-wall thickness on my Greener .577 is 0.260 inch at the breech-face.