Hi,
Probably every new builder on this sight has posted the same question. There are many finishes that work well. BLO sold today in hardware stores is linseed oil mixed with solvents to speed drying. It is not the same as what was traditionally called "boiled linseed oil", which was actually an oil varnish. It contained some sort of resin to create a varnish and was much more weather resistant than pure linseed oil. Pure oils like linseed or tung take forever to dry and no old time or modern gunsmith can afford to spend months on a finish that ultimately is mediocre. Mixing linseed oil with a varnish like spar or polyurethane will work well, dry quickly and looks a lot like the old BLO finishes. Tried and True makes a fine linseed oil varnish that many top gunmakers use. Another option is to heat treat (polymerize) the oil and mix with solvents. Tru Oil is just linseed oil polymerized and mixed with solvents and works pretty well. You can also get polymerized tung oil, which is even better. Sutherland-Welles is one brand and is the finish I use. There are also synthetically produced finishes such as Permalyn that are popular although they can impart a plastic look to the finish if built up too much. In my work, I want a finish that is reasonably weather resistant, can be repaired if needed, and looks like the old finishes found on original guns. Here are examples of guns finished with polymerized tung oil.
The look ranges from somewhat glossy to a low sheen depending on my objectives.
dave