What Miller said. I value working grade guns, but, nothing would turn me off faster than a London blacking job on the barrels of a NItro, Tobin, Trojan, or Sterlingworth.
I think that most R grade Darnes were out to 400 grit, or so, and the V grades might have went to 600, more if a customer requested it. The steel was XTC, a Fench tool steel on the order of 4140, but, higher in chrome, and tough to blue.
They had a nice, dark, black finish on the tubes in the era I was involved with it. I really liked it.
Our own Ken 61 did some very nice, factory level blue on my Nitro. He wanted to take it out further than 320. I told him absolutely not, and am beyond satisfied with the finish he did.


Best,
Ted