I have done them all at various times over the last 40 years. In the early years I used plum brown and I do like the results. Later tried acid browns and the sweat box not my favorite. Often rather spotty and required lots of time. The cold blues worked for touch up situations or small parts but never lasts under moderate use on the larger parts. I have heard about builders using vinegar. I have never tried so can’t comment. For the last four builds I am bluing, but using a commercial (Brownells) blue process. It copies the old Belgian blue often used on soldered English dbl barrel shotguns. This process requires meticulous metal prep. Follow up application with the blueing liquid and boiling in water, repeated at lest seven times. Easily done in the home setting, but may require purchase of special equipment if one is not handy. Final results are a deep dark blue black finish. For the French blue I only repeat two times and vigorously rub back to bring down the blue.