Oc

ric. 112 246

front of the reamer. This pilot is ground and polished to be a push fit on the top of the lands. There are also stop guides at the rear of the reamers to show when each has been run into the chamber deeply enough.

The finishing reamer, that is the final one used, must be ground to very close dimensions, and it is this reamer also which cuts the bullet sett or leed. The bullet seat is that portion of the chamber ahead of the mouth of the case, into which that portion of the bullet projecting out of the brass cartridge case fits. It should be cut so that the ogive of the bullet, that is the curve of the point, will just barely touch the origin of the lands, and the beginning of the landi should be cut on the same curve or slope as the ogive of the bullet. Usually there is a short portion of the chamber ahead of that portion corresponding to the mouth of the case, which is cut cylindrical and smooth by simply reaming out the lands, leaving this portion a true cylinder of groove diameter. This cylindrical portion receives the portion of the bearing or maximum diameter of the bullet which projects outside of the case. Then ahead of this the lands start on a gradual slope.

Generally speaking, the best accuracy is obtained, other details being correct, when the cartridge and bullet are so shaped and assembled that there is a portion of the cylindrical, maximum diameter of the bullet projecting beyond the mouth of the case, and fitting with almost a push fit into the cylindrical portion of the bullet seat. Then the bullet scat straightens the bullet up so that its axis is in line with the axis of the bore, and thus on discharge the bullet slides straight forward into the bore and rifling without any wobble or jump which might tend to deform the bullet.

That portion of the chamber corresponding to the neck of the case should be a little longer than is necessary from the measurement of the cartridge. That is about 1/32 to 1/16 inch should be allowed for the lengthening of the neck of the case, and the shoulder of the chamber ahead of the mouth of the case should be pushed forward correspondingly. Cases lengthen considerably when fired, particularly cases which have been reloaded a number of times, and the chamber must allow for this, or it will actually crimp the cartridge just as a reloading tool docs, and this may lead to ragged shooting or even to excessive pressure.

Only experienced tool-maker» have the art and skill necessary to make chambering reamers. Such a roan will readily understand the instructions and explanations herein. If the gunsmith is not also a tool-maker he will be obliged to have his chambering reamer» made for him, preferably by a firm of rifle barrel makers. The making of a tet of chambering reamers is expensive work. Besides the time of the designer, and of the workman, muck machine time is necessary, and thus the cost of making one complete set of reamers and the accompanying he ad space gage» will run aomewkere between

Was this article helpful?

0 0

Post a comment