Before starting work at all, ask yourself the question: Do I NEED to take this gun apart? Due to the fine workmanship in originally fitting the parts, and well over a hundred years of buildup of minute particles of grease and dust in the crevices, and just plain overall "patina", it can be quite difficult to separate the metal from the wood, and there is a significant risk of chipping the stock in critical areas.
If, for whatever reason, you HAVE decided to proceed, perform the work in an uncluttered area, with good light, and be sure you have the proper tools at hand. These would include: properly fitting screwdrivers for each size screw to be dealt with, a light hammer, penetrating oil such as Liquid Wrench or WD40, several small blocks of hardwood approximately 1" x 1" x 3", rags, and a selection of pin punches. A padded cradle, built of scrap wood and carpet, can be useful for some operations where it is helpful to have both hands free. The Model 1879 combination tool will come in VERY handy. They are inexpensive enough to keep several on hand. But, by far the most important commodity is TIME. Do NOT attempt to take a fine gun apart in a hurry!!
Following instructions should be performed pretty much in the order stated.
(1) Remove the cleaning rod. On most arms, this entails pulling the tip of the rod away from the barrel to free it from the stop, and then forward. (on the M1865 it will pull straight out - on the M1866 and M1867 Cadet (lucky you!) it must be unscrewed before withdrawal). On the M1880 and M1882 TRB models, slide keeper (if present) to the left, press thumbpieces against barrel and withdraw rod. On the M1884 and 1888 RRB models, press on the checkered thumbpieces to withdraw the rod.
(2) Remove the barrel band(s). Loosen the tang screw a couple of turns, NO more. Depress the band springs and push the band(s) forward with your thumb. (CAUTION: if dealing with a carbine, the gun will be free to start separating, and care must be taken to prevent sudden motion to cause a split at the tang). CAUTION: this operation may cause scratches. If the bands do not want to come loose, apply penetrant (WD40 does not seem to bother wood) and use the light hammer and hardwood block to start them, alternating from side to side (this is one operation where the cradle can be very useful). On the M1868 rifle, if the lower band does not slide off, you can loosen the clamping screw; otherwise leave it alone. With 1888 RRB Rifle, the bands will NOT pass over the latch, thus barrel removal is a bit different.
(3) Bring hammer to half-cock (assumes lock still installed). With the gun restrained against sudden motion, carefully unscrew the tang screw further, at the same time carefully raising the muzzle end of the barrel from the wood. Some people like to invert the gun, and let the barrel "fall" out. It does not make a great deal of difference HOW you do it, the key is to go SLOW and do NOT let it come out crooked, levering off a piece of wood at the tang. Some guns will be stuck so tight that they resist your efforts and then suddenly "pop" loose. That is why you need to have the parts under control. The M1888 RRB, because the bands do not come off, requires a slightly different technique in that the tang end has to come out first, so that the bayonet latch housing can be slipped forward off the stock tenon. After working the bands as far onto the latch as you can, fully remove the tang screw, and invert the gun, keeping your hand wrapped around it. If it doesn't come out, you'll have to open the breech and use the block as a handle. If this is the case, be VERY careful to pull it STRAIGHT out.
(4) Set the stock, and all attached parts aside, carefully.
(5) We will now deal with the barreled action. To remove the (M1868 through 1888) breechblock assembly, tap the tip (right side) of the hinge pin, twist its arm and pull it SLOWLY to the left. If you only want to remove the block, without dealing with the extractor and ejector, only withdraw the pin enough to allow the block itself to be pulled loose. The other parts will remain captured on the hinge pin. If you need to replace, say, the ejector spring; then pull the hinge pin all the way out. The extractor, ejector, ejector spring, and ejector spring spindle will now fall clear, or can be picked out. The removable, surface-applied, extracting/ejecting parts of the Model 1865 and 1866/67 models are self-evident. Unless ABSOLUTELY necessary, the breechblock mountings of M1865 and M1866/67 arms should NOT be dismounted - the bases are soldered to the barrel; removing the strap screw(s) will release nothing. The screws are often VERY tight, and are easily buggered.
(6) IF you need to dismount the breechblock, remove the breechblock cap plate screw, which will release the plate, the thumblatch/camshaft, and the cam spring. To remove the firing pin, undo the screw on the bottom of the block, and, hopefully, shake the pin out. Firing pins are frequently tight in their holes, and really should be left alone unless broken (easy to determine, a good pin will slide as a unit, a broken one will either be jammed or exhibit independent movement of the separated front and rear pieces). A broken pin can be a problem, which may require significant work. Model 1865, and early Model 1866 arms have the screw which retains the camshaft on the LEFT side of the block. On Model 1865s, the firing pin and spring are retained by the tiny screw on the side of the block. On Model 1866/67 arms, the firing pin is retained by a slotted nut, which needs a special spanner. This can be found on some of the armory tools (other than the 1879) or, in a pinch, made by hand by grinding a notch in a wide-bladed screwdriver.
(7) The rear sight should, in most cases, be left alone, and on the barrel. Screws are small and easily damaged. In the case of M1873, M877, and M1879 sights, if you are fortunate enough to have the original unslotted attaching screws, they should be left strictly as-is. If they MUST be removed, try the three "P"s (penetrant, padded needle-nose pliers, and PATIENCE). Barrel should be held in a well-padded vise - this is one place where you do not want to slip. Those arms utilizing the musket sight, or the 1868/70 sights, will require the use of a special spanner.
(8) The front sight on early arms (on rifles, up until around 90000 in the Model 1873 series) is not removable. On those front sights which do have a removable blade, the pin should be pushed out from the left side, they ARE tapered. On the Model 1884 RRB (ONLY) the front sight is mounted to the removable hood, NOT the barrel. This can be removed by driving out the pin which goes through it and the barrel.
(9) Latch mechanisms of the round rod bayonet models, while removable, are best left assembled, particularly the Model 1884. They were put together using special jigs, and are under heavy spring pressure. If you must, clamp the barrel, from top to bottom - putting a squeeze on the mechanism, in a well-padded vise. Drive out the pin - then SLOWLY undo the vise. Pay attention to the orientation of the parts. Do not lose the small coil springs under the thumbpieces of the Model 1888.
(10) We will now turn to the stock and other parts which were set aside. First let us deal with the small items of "furniture". Band springs, unless broken should be left alone. If they need to be removed, secure stock on a flat padded surface, and, using your M1879 tool, or punch of same diameter, gently, SLOWLY, and above all, carefully aligned, so as not to oval the hole, tap the spring out from the left side. CAUTION: Watch what you are doing, as this can cause chipping. If the cleaning rod keeper is broken (not uncommon, and easily determined) it can be removed after taking out the band spring pin as above. The tip is held by a small screw, which is often rusted, but this is another part which should be left alone. The buttplate is held by two screws, which are often rusted/frozen. Only remove them if you must, working slowly and carefully to avoid having the screwdriver slip. A rounded tip, such as on the M1879 tool, is helpful in eliminating slips. The lockplate screw escutcheons should DEFINITELY be left alone as they are often deep-seated, VERY tight, and there is NO good way to get at them - they were intended as a one-time installation.
(11) Now for the most difficult, and often troublesome, part of all - that of removing the lockplate and the trigger guard. More harm is done to otherwise fine guns, by getting this part wrong, than everything else combined. Refer to the note at the beginning - do you REALLY need to do this? IF the answer is "no", then LEAVE IT ALONE. The key to getting these parts out safely is to use a method which allows the application of (occasionally considerable) force but ONLY that which can be applied against restraint; this eliminates the possibility of a sudden uncontrolled movement. If you must proceed, the first step is to bring the hammer to at least half-cock - the .safety. position (on later locks) MAY not be enough. This is CRITICAL because it will assure that the mainspring is compressed enough to clear the bottom edge of the lock mortise, on the way out. Failure to perform this simple act is the cause of the many nasty stock chips found below the lockplate. Second step is to unscrew the lock screws a couple of turns - NO more at this stage. With your hammer and wooden block, tap alternately on the heads, all of the time watching very carefully to see that no chip or flake is starting at the edge of the plate. If your lockplate slips out freely, count yourself lucky. If not, keep up the tapping (you'll have to gradually loosen the screws) until it is all the way out. Do NOT grab the hammer and attempt to pull, or lever, the plate out! Set the assembled lock aside for now.
(12) For some reason, the trigger guard is usually the hardest part to remove safely. It is also one of the least necessary parts to remove, so, my standard advice applies - if you do not need to remove it - don't. If you must, the best way that I have found is this: Install the tang screw part way. Undo the guard screws a half turn - full turn, maximum. Tap on the tang screw with your block and hammer, or plastic mallet, observing how the guard reacts. If it moves, and no chips (particularly watch the front) start, proceed gradually, undoing the screws a little at a time, to tap it out. Above all, you MUST resist the temptation to pull it out using the curved bow. A VERY small amount of rocking side to side may help, but ONLY if necessary. Yes, I am aware that on a worn gun, the guard will fall out of its own weight, but remember that these instructions were written with higher-grade pieces in mind. The trigger guard my be disassembled by removing the nuts (except on a Model 1888). The trigger is held by one small screw. The lower swivel, if retained by a screw (some are riveted) may be removed if required.
(13) The first step in disassembling the lock is to remove the mainspring. This is accomplished by bringing the hammer to full cock, after which the mainspring must be captured. This can be done in several ways, depending on whether you need to have the spring loose or not. If you have no need to let the spring relax, the notch on the M1879 tool will perform as designed. A better choice is a mainspring vise, and least desirable, but workable, is a pair of large vise-grips. Next step is to loosen the sear spring screw enough to allow the spring to be lifted from its slot; when it is free, remove the screw entirely. Then remove the two screws holding the bridle - keep them in order, note that lengths are not the same.
Next, the tumbler must be removed FROM the hammer - note carefully what I just said, the hammer is NOT to be pried off the tumbler! Remove the hammer screw, CAREFULLY, they are frequently VERY hard to start, and any buggering of this screw, or slipping of the driver onto the lockplate will be VERY noticeable, and needs to be avoided at all cost. A padded vise and penetrant may be required. When the screw is out, rest the lockplate, face up, on two of your blocks of hardwood, placed as close to the tumbler as you can, insert the punch portion of an M1879 tool (this is why having more than one is desirable) into the tumbler, and give it a good whack with your light hammer. Hopefully that will separate the parts. If not, let it soak in penetrant and try later. If your only M1879 tool is occupied by the mainspring, use something else as a punch, being careful not to damage the tumbler. In a pinch, you can use the hammer screw, partially threaded in, but this is NOT recommended as a first choice, and if used, the whacking (using a wood block or plastic mallet) should be considerably gentler.
Reassembly is, in most cases, a simple reversal of the above.