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which have no tight or loose places, but have even diameters from breech to muzzle, although roost riflemen have the opinion that a rifle to shoot lead bullets exclusively will do better work if it gets just a litde bit tighter towards the muzzle, being gradually tapered.

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 its exact center. In this hole place a piece of straight wire, about .0625-inch in diameter. Press the cork into the chamber and un about half an inch into the rifling, so that the wire extends through

A F'. N ISii ED SULPHUR (.HAMHKK CAST

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 for the cast is made of the following materials:

Sulphur .

Gum camphor dissolved la alcohol

2 ounces

3 jr rains I 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. This cast can now be measured with a micrometer and scale, and will give the dimensions of the chamber as well as its 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.

TWIST OF RIFLING: The table on the previous page in Chapter 15 shows the twists of rifling which have proved best for various calibers and cartridges as a result of years of experience. The lower the muzzle velocity, the longer the bullet, the poorer the quality of the bullet, and the longer the range at which accurate results are desired, the quicker the twist of rifling must be to correctly spin the bullet so that it will keep point on and fly accurately.

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