I used to have one of the Nepalese-made 'Brunswicks' with the 2-groove rifling. I had a local m/l gun building friend remove the breech plug for me, as I'd heard all kinds of stories about the quality. We were both pleasantly surprised by the quality of the thread as it seemed to be machine cut & very well done, though a little coarse (tpi-wise) in my friend's opinion. The rifling is another matter altogether, as it ran very non-uniformly in either depth or pitch. As you may know, the Brunswicks were intended for use with a belted ball which fit the grooves mechanically, but there is no way in heck that a belted ball would be able to follow that rifling down the bore! As far as the nipple was concerned, I was expecting to find that it would be a close approximation of the standard British 5/16x18, but instead found a nipple with a smaller diameter shank cut with a very coarse & un-uniform thread. We fixed that by drilling out the hole to 5/16" & threading it with a 5/16x18 tap.