The following information on preventing handgun misfires comes from Section 22 of Shooting by J. Henry FitzGerald. Shooting is also available to purchase in print.
A misfire is not always the fault of the revolver or the cartridges. In many cases it is caused by the cartridges remaining in the chambers so long that the oil finds its way to the powder between the bullet and the shell. This is called an oil-soaked cartridge. Oil or water may work in through the primer socket and destroy the fulminite in the primer.
A good rule for protection is to change the ammunition every four weeks. If ammunition is not available in quantities to allow this, at least change the first two cartridges to be fired. One is then assured of the first two shots and the ammunition should never be more than three months old. If care is taken to allow only a thin film of oil to remain in the cylinder the cartridges will be dependable when three months old.
Misfires which we cannot guard against are the ones caused from defective primers. I have found many without the anvil, and no powder in the shell. I have found a great many shells without an opening from the primer socket to the powder chamber and these are very dangerous if the arm is opened before the primer cools. I have several times received a cut on my face by swinging the cylinder out too soon. It is dangerous to open and examine any revolver immediately after a misfire. At least twenty seconds should elapse before the arm is examined. A misfire might result from a deep set primer which the firing pin will not reach, and this fault may be easily discovered if the shells are examined.
Another very frequent error is made by persons not accustomed to the use of firearms. When they are firing double action the trigger must be released after each shot to allow the parts to fall back in place ready for the next shot. I have seen many such cases where the shooter claimed that the arm was defective. If single action is used the trigger must be released after each shot, otherwise the cylinder will not turn and the hammer will fall on the exploded shell. This is a very common occurrence, but the recoil will usually take care of this trouble if the arm is not held too tightly.
Another source of misfires is from the revolver used for target shooting single action with the spring lightened to aid in cocking of the hammer. Due to the longer hammer fall when fired single action no misfires will occur, but before this arm is used for quick protective work it should be thoroughly tried double action to make sure that no misfires will occur.
Misfires may also be caused by using a heavy oil in the mechanism. I once discovered a revolver with the mechanism lubricated with LePage’s glue mistaken for gun grease. Neither heavy oil or gun grease should ever be used; on rare occasions a drop of sperm oil will aid the working parts. If the arm is dropped in the water or mud it should be taken apart and thoroughly cleaned and each part wiped over with an oily rag; before replacing side plate, oil the working points, such as trigger, hammer pin, safety, etc., with a toothpick.
In target shooting when the thumb is placed high on the frame be sure that the pressure is not exerted against the side of the hammer to the extent of slowing up the action and thus causing a misfire.
Oil the firing pin and note whether a pierced primer or moisture has caused it to rust, for if it has rusted or corroded it may not fit the firing pin hole and such rust or corrosion may form a cushion on the end of the firing pin and cause a misfire. The firing pin hole through a pierced primer or moisture may be coated with rust and cause the same result.
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