gage. The bolt handle should turn down on this gage with just nv di in operating the rifle and having the cartridges insert easily in rapid a slight suspicion of feel, but not so hard as to cause any difficulty ring fire. At the same time the bolt should not close down completely on the "NO GO" gage. Figure 115 shows the two headspace gages, "GO" and "NO GO" for the Springfield rifle.
The minimum headspace gage for the .30-06 rifle and cartridge is known at the 1.940 gage, that being its length from a determined point on the cone to its head. The bolts of all rifles for 30-06 cartridges, military or sporting, must close readily on this gage. The "NO GO" gage for arsenal use is known as the 1.946 gage, being .006-inch longer than the minimum of "GO" gage. Bolts of rifles issued from arsenals must not close completely on this gage. The "NO GO" gage for rifles in the hands of troops is known as the 1.950 gage. If bolt» of rifles in the hands of troops or in storehouset at posts close on this gage when they are inspected such rifles are withdrawn from use and issue, and are sent to an arsenal for repair».
Headspace gages, as a rule, cannot be bought, but must be made by the gunsmith, or by the man who makes the chambering reamer», from ground and hardened steel. When a gunsmith has a number of barrels of a given caliber to chamber or fit he should certainly have a set of gages for that caliber. He is then prepared to fit ready made and chambered barrels of that caliber to any breech ac tion. For example, if he has a set of such gages for the .30-06 cartridge he may buy his barrels ready chambered and threaded from the several sources of supply for such barrels, and he can then screw these barrels directly to his receiver, and then he can proceed to try different bolts in that rifle until he finds one bolt which will dose down on the "GO" gage, but will not close down on the "NO GO" gage. That barrel, receiver, and bolt arc then perfectly satisfactory and have the correct headspace.
But if the gunsmith has but one barrel to fit he may be able to get by with it all right by using a loaded cartridge as a gage. Procure a number of cartridges of different makes of the caliber desired. Select from this lot by trial in another new rifle of standard make the two cartridges which appear to be the largest and longest. It will be difficult or impossible to measure their length from shoulder to head if they are rimless cartridges, but one will probably be able to tell by the way they feel when they go in the standard rifle, and the way the bolt closes on them. Use one of these for the "GO" gage. Paste a disc of paper .005-inch thick, on the head of the other and use it for the "NO GO" gage.
The gunsmith, and all riflemen in fact, must beware of the ready chambered and threaded barrel. It cannot be stated too strongly that rifle barrels cannot be made strictly interchangeable, and that the only way a ready made and completely chambered and threaded barrel can be safely fitted to a rifle is by changing breech bolts until one is found which fits tightly enough (and not too tightly) to successfully pass the gaging test, or by carefully fitting the breech block or bolt in an unfinished state, machining or grinding it to a perfect fit with the gage.
The reason why barrels cannot be made to be interchangeable is shown in Figures 114-C and 114-D. To assemble interchangeably it would be necessary that the sum of the measurements B, C, and D be not greater than the difference between the minimum and maximum headspacr permissible. But in production no one of these measurements can be assured closer than, say, .003-inch. Thus, if in a given barrel and receiver and bolt, these three measurements were all maximum, or all minimum, we would have an aggregate of .009-inch, whereas in most rifles the maximum permissible difference between max. and min. headspace is about .006-inch. The barrel is therefore always finish chambered after being assembled to the receiver and bolt in connection with the headspace gage.
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