screw fairly easily to within about 1/4-turn of meeting of index lines, and should then require a heavy wTench to screw entirely home. The "index lines" are the two short, almost invisible lines, one cut in receiver, and one in barrel, which meet exactly when the barrel is screwed entirely home into the receiver. The assurance of correct headspacc and security of barrel in receiver are the most important reasons for seeing rhat barrel is screwed exactly to index lines, but also if front and rear sight bases have previously been mounted on the barrel, then these should stand truly vertical when the index lines meet.
If it is impossible to get the index lines to meet when the barrel is screwed up forcibly with a long wrench, then instead of easing up on the threads to give them more tolerance than is allowed in good machine practice, the face of the shoulder on the barrel should he lightly squared off until they do meet. Some barrel makers lay great stress on the fitting of this shoulder to the end of the receiver ring, and employ the "spotting" method to secure perfect contact. One celebrated barrel maker maintains that best accuracy, particularly in .22 caliber match rifles, is obtained when the entire surface of the barrel shoulder is in perfect contact with the end of the receiver, with equal pressure at all points. To "spot in" a barrel, the end of the receiver which bears "against it is very lightly coated with Prussian blue, and the barrel screwed in fairly tight; then remove it and note the spots of contact. Dress them off carefully with very fine files—a 3-inch die-sinker's needle file will usually serve; or some of the various die-sinker's rifflers as made by the American Swiss File Company. Continue the spotting and test-fitting until the contact is perfect when barrel lacks about 1/16 inch of being screwed up; then give the wrench the final twist which sets it all the way.
Figure 111A shows a good type of wrench to use in screwing barrels into and out of receivers. It is made by welding or brazing a piece of tool steel to the upper jaw of a large monkey wrench, with handle from 18 to 24 inches long. The notch in this false jaw is cut at an angle of 90 degrees, giving it two-point contact on the round, upper portion of front end of receiver. The flat lower jaw bears against the flat portion found on the under side of most bolt action receivers, and the wrench should be screwed up rather tightly. It is advisable to drill four to six 1/8-inch holes in the set-screw of the wrench so that it may be tightened with a short length of drill rod. The surface of both jaws of the wrench should be polished off smooth to avoid marring the receiver, and the jaws may be modified as desired to obtain purchase on receivers of various types, Most lever action and single shot receivers have two flat surfaces on either side on which a standard long monkey wrench without modification of jaws other than to polish them, will take hold. 239
Never, hold the receiver in a vise and screw out the barrel when it can be avoided. Rather hold the barrel in th'e vise and turn the receiver with the wrench. A good inexpensive method of holding the barrel in the vise so that it will not be marred is as follows: Take a piece of Shelby tubing, 4 inches long, with inside diameter slightly smaller than barrel near the breech, and walls about 1/4
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