Continuing from the previous posts, the HEIGHT of a nipple is the dimension from where the flange seats against the cylinder to the tippy-top of the conical section of the nipple. Or, if you prefer, the total length of the nipple minus the length of the threaded section, will give you the nipple HEIGHT. Having nipples of the correct height is important for consistent cap ignition.
Before getting into the details of this discussion, it will help to agree on what is the proper nipple height for a particular revolver.
Most gunsmiths advise that, with a nipple of the proper height in place, the hammer face will not touch the nipple, even when pressure is applied to the hammer when the hammer is down—this is called under-travel. If it does touch, this is undesirable and is called over-travel, which will cause wear, damage or even breakage to the nipple and hammer. Note that it is not necessary for the hammer to ever actually impact the nipple in order to ignite the cap. Changing the nipples for shorter ones is one way to alleviate this problem. For later, keep in mind that hammer under-travel/over-travel can be adjusted in other ways, if all other options fail.
The reason the caps will still fire without the hammer actually striking the nipple is because the thickness of the percussive material in the cap and the foil of the cap is somewhere in the neighborhood of .040” to .050”, depending upon which brand cap you measure. Here are some cap thicknesses I have randomly sampled. To do this I first measured the total LENGTH of a short piece of metal rod that all of the caps would fit on loosely (fully seat). Then, with the cap in place, I measured again. (For the photos I used a star bit for the probe.)
The difference between the readings provided the dimensions listed here for the thickness of 4 different brands of percussion caps:
Top of cap rests above top of nipple by;
Remington, about .042”
CCI Magnum, about .050”
Winchester Magnum BP, about .050”
RWS, about .047”
Theoretically, you could have hammer under-travel of .020” to .040” and the cap would still fire. In practice, it probably is best to keep it between .010” and .030”.Hammer Clearance Test
At this point it will be helpful to have a “feeler gauge.” This is a tool which allows you to measure very narrow gaps. In C&B guns this tool is used to measure the flash gap, which is the distance between the barrel and the cylinder face when the cylinder is pressed as far rearward as it will go.
How do you test for this? With the hammer down—under firm thumb pressure—you should still have most, if not all, of the flash gap you had when the hammer was at half-cock. If you have .005” flash gap at half-cock, you should still have .005” flash gap with the hammer pressed hard down. But if you have a large flash gap—say .018”—then it might be acceptable to have only .010” with the hammer down hard.Test if Nipple Stands too High
A quick test to see if a nipple sits too high is to press the hammer down hard with your thumb and see if it drags on the nipple by wobbling the cylinder against the stop (bolt). If it drags on the hammer, the nipple sits too high. Here are the results of a test with 6 Remington New Model Army (1858) revolvers:
Gun (Yr) FlashGap@Half-cock Gap W/Hammer Down Result
R29 Pietta (2001) - .006” - - - - - - - - - - - .000” - - - - - - - - - - - - - Drags
R37 Pietta (2007) - .005” - - - - - - - - - - - .000” - - - - - - - - - - - - - Drags
R41 Pietta (2011) - .008” - - - - - - - - - - - .000” - - - - - - - - - - - - - Drags
Santa Barbara (72) .009” - - - - - - - - - - - .009” - - - - - - - - - - - Does not drag
Navy Arms (1967) - .006” - - - - - - - - - - - .006” - - - - - - - - - - - Does not drag
Uberti (2012) - - - - - .003” - - - - - - - - - - - .003” - - - - - - - - - - - Does not drag
(The Navy Arms is an early Uberti)
If the gun passes the test with the flash gap being the same at half-cock as with the hammer down hard, that is great, but there might be the opposite problem . . . the nipple could even be too short. You can’t know unless you perform the following test.
Test if the Nipple Sits too Low
To test if a nipple’s height is too low, back the nipple out of the cylinder by a quarter turn and retest. Continue this until the nipple drags on the hammer. A quarter turn is about .007” to .009” +/-, depending on the thread pitch. To figure this exactly for a given nipple pitch, here are some examples:
For a 12-28 tpi thread pitch:
1.000” / (28 X 4) = Height added by ¼ turn = .009”
For a 6 X .75mm thread:
Tpi = 25.4mm / .75 = 33.87tpi
1.000” / (4 X 33.87) = Height added by ¼ turn = .007”
For a 5.5 X .9mm thread:
Tpi = 25.4mm / .9 = 28.22tpi
1.000” / (4 X 28.22) = Height added by ¼ turn = .009”
Note that all nipples on a cylinder should be tested this way as you will often find one or more nipples may sit higher or lower than the others (there could be several causes for this problem, which will be discussed later). Once you have made these tests and have established whether your nipples are the correct length, or too long, or too short and by how much, you should next establish the actual dimensions of the nipples in your gun by measurement.