Who doesn't love a good gun cleaner/gun oil discussion?
I've used a lot of commercial gun cleaners, and also a lot of non-commercial gun cleaners as well as "traditional" things that aren't advertised as such but are common.
Many of the common cleaners are some sort of petroleum distillates(i.e. mineral spirits, naphtha) with some other stuff added in. Among the common ones, Hoppes #9 has isoamyl acetate(synthetic banana fragrance) and a small amount of ammonia to help dissolve copper fouling. Hoppes Benchrest #9(a bit harder to find) is loaded with ammonia and also-I think-has some glycerin or something similar to make it "clingy." I've found that it works well to clean heavy copper fouling, but my usual application method is to saturate a nylon brush, make a couple of passes, plug both ends of the barrel with a patch, and wait. A few hours later, you will push out a half dozen or more dark blue patches. If you can still see orange streaks in the rifling, apply again. I don't find Hoppes #9 to be particularly offensive(in fact I rather like the smell) but Benchrest #9 absolutely reeks. Most other dedicated copper cleaners have high ammonia or amine contents that make them equally vile, but they're really the only way to get heavy copper out without a lot of elbow grease.
WD-40 has some merit as a simple powder solvent. Its base is Stoddard's solvent-not a lot different from what's used in Hoppes and others-but it has a waxy component that tends to congeal and cause issues over time. If you spray some in a small, clear container and leave it overnight, you'll see what I'm talking about. Like most other light petroleum distillates, it can "creep" under lead fouling and help to loosen it, although you'll still need some mechanical action to actually remove lead(a snug bronze bronze brush, bronze wrapped in chore boy, a very tight patch, or even a stainless Tornado brush in extreme cases).
Someone mentioned jet fuel above. Jet A is actually pretty darn similar to kerosene although a lot more expensive. It actually makes a good cleaner for general powder fouling, but if you're going to use it get white kerosene at a gas station(~$4/gal or so the last time I bought some). I keep a 5 gallon can of kerosene in the garage for a multitude of uses. I use a kerosene heater in the winter to keep things tolerable. A kerosene lamp without a chimney and with the wick turned up high is-I've found-just the ticket to "smoke" a bullet mold(those of you who cast will know what I'm talking about). It's a cheap and effective degreaser in automotive applications where you don't necessarily need surfaces scrupulously clean, and also leaves some lingering rust protection.
Starter fluid-or at least what I'm familiar with-is primarily ethyl ether. In my time as a bench chemist and organic lab professor, I've handled enough of it that being around it very long gives me a headache and makes me physically ill. The flash point is extremely low, so be sure you keep things well ventilated and avoid any source of open flame. We have non-sparking light switches in labs at work for this reason(they're actually old enough to be mercury tilt switches). As the department safety officer, I've been called to ether fires more than once. The last one was actually quite spectacular-a student was boiling it in a beaker on an open hotplate and either the stirring motor in the plate sparked or there was some part of the plate that was over the auto-ignition temperature. In any case, I happened to be walking by and heard a "pop" followed by a couple of screams-I walked in and saw a fire ball about 8" in diameter and 2' tall on top of the hot plate. Fortunately, no one was hurt and the fire burned itself out in a minute or two, but once things had settled down and all the paperwork taken care of, both the teaching assistant in charge and the student got a serious talking to(I hauled the TA into the chair's office).
I've used a couple of different foaming bore cleaners. I've found many of them to be good on copper fouling. Most of the ones I've looked at use a largish amine to complex the copper. This has the side effect of also making them very "sticky". They really cut whatever [censored] is in the barrel, but in my experience cleaning up after them takes a fair bit of work also.
I'm a big fan of Ballistol(I still maintain that they should put Hickok45 on their payroll). It's more of a mineral oil, which makes it a decent all around CLP. One of the major additives is oil of anise, which gives it the distinctive licorice smell that folks either love or hate(I don't mind it personally). It also has something-I'm not sure what-that will dissolve light copper deposits. A few hours will give you green streaks on a patch, although don't expect it to work miracles on copper. Hoppes is better, and a dedicated copper solvent is even better than that. One place it really shines is as an emulsion with water("moose milk") that does one heck of a good job on black powder fouling as well as corrosive primer residue. As these are some of the most destructive things you can leave in a gun, I treat both with moose milk immediately. For black powder, I often take some to the range with me(especially on humid days) and swab the gun with it until patches come out clean before packing up. The gun, of course, gets a full disassembly and scrub down when I'm home.
I've used my fair share of 3-in-1 oil as a gun oil. I've found it to work great both as a lubricant and rust protector. Rust protection is important to me since most of my guns are traditional(hot blue) carbon steel with a few nickel carbon steel guns mixed in. Of course, I also have parkerized carbon steel, stainless steel and alloy, but the blue guns are my priority since they're the least tolerant of poor storage. They also look great with a fresh coat of oil on the barrel-particular a nice high polish Smith and Wesson.
Aside from that, I've tried a fair number of "gun oils" including Rem Oil and some sold under the Hoppe's brand name. Most I've been pretty neutral on-neither good or bad, but perfectly serviceable. I go back to 3-in-1 because-to me-it's hard to beat the smell of a gun cleaned with Hoppe's and oiled with 3-in-1. Fire off a few rounds of Unique and you have an unbeatable olfactory sensation.
