Snidely70431
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- Mar 10, 2018
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I have noticed several threads about measuring bore size of muzzle loaders that often seem to involve pounding lead into the bore. I remembered an old gunsmithing book has a section about measuring chambers, a technique which should work with bore sizing. This is from Clyde Baker's Modern Gunsmithing, copyright 1933:
MEASURING CHAMBERS. To measure the chamber of a rifle it is necessary to make a sulphur cast. The chamber, and about one inch of the rifling forward from it, should be thoroughly cleaned and then covered with a very thin film of light, clean oil. Take a cork the size of the bore of the rifle and drill a small hole through the exact center. In this hole place a piece of straight wire about .0625-inch in diameter. Press the cork into the chamber and up about half an inch into the rifling, so that the wire extends through the cork and back to a point several inches in rear of the breech. The wire functions as a handle for the cast as the cast is very brittle. The mixture of the cast is made of the following materials:
Sulphur ............................................2 ounces
Powdered lamp black.........................3 grains
Gum camphor dissolved in alcohol.....3 drops
Heat very slowly and stir continually. When the mixture arrives at a thin pouring consistency, pour it into the chamber quickly, and allow to cool thoroughly before removing. To remove, place a rod in the muzzle and shove lightly on the cork, letting the cast come out slowly, and handling it very gingerly as it is quite brittle. The cast can now be measured with a micrometer and scale, and will give the dimensions of the chamber as well as the shape. The mixture is almost shrink proof, but it is well to allow .0005-inch for shrinkage if measured at once, or .001-inch if measured a day after cast. It is important that the mixture be heated slowly, otherwise it becomes too thick to pour.
MEASURING CHAMBERS. To measure the chamber of a rifle it is necessary to make a sulphur cast. The chamber, and about one inch of the rifling forward from it, should be thoroughly cleaned and then covered with a very thin film of light, clean oil. Take a cork the size of the bore of the rifle and drill a small hole through the exact center. In this hole place a piece of straight wire about .0625-inch in diameter. Press the cork into the chamber and up about half an inch into the rifling, so that the wire extends through the cork and back to a point several inches in rear of the breech. The wire functions as a handle for the cast as the cast is very brittle. The mixture of the cast is made of the following materials:
Sulphur ............................................2 ounces
Powdered lamp black.........................3 grains
Gum camphor dissolved in alcohol.....3 drops
Heat very slowly and stir continually. When the mixture arrives at a thin pouring consistency, pour it into the chamber quickly, and allow to cool thoroughly before removing. To remove, place a rod in the muzzle and shove lightly on the cork, letting the cast come out slowly, and handling it very gingerly as it is quite brittle. The cast can now be measured with a micrometer and scale, and will give the dimensions of the chamber as well as the shape. The mixture is almost shrink proof, but it is well to allow .0005-inch for shrinkage if measured at once, or .001-inch if measured a day after cast. It is important that the mixture be heated slowly, otherwise it becomes too thick to pour.