THREAD 12 TPI
The bolt, constructed from the same material as the barrel extension (4130, 4350), is only slightly more difficult than those built for smaller actions. It's just larger and takes longer. However, several drill extensions must be made up to drill the firing-pin hole through the bolt.
With the ends of the blank squared, a small hole is started through one end using a #2 center drill. This is then enlarged and lengthened with a 3/32-inch (.087-inch) drill. This will provide the opening in the bolt face for the smaller end of the firing pin. Drill this to a depth of 3/4 inch or so. The drill used here, as well as all the others used in this bolt construction, should be new and sharp. When in use, they should be withdrawn frequently and cleaned and relubricated. A counterbore, two hundred thousandths of an inch deep and to a diameter that will just accept a case head, is machined in the bolt face. The bolt face so formed must be very smooth.
While chucked in this position, the bolt body should be turned to a diameter of 1 1/2 inches (1.50 inches), as shown in the drawing, and the groove should be cut to form the flange that forms the locking lugs. The rear side of this groove should be very smooth and square with the bolt body. The rest of the bolt body could be kept at a constant 2-inch diameter. But turning it as shown and adding the outer sleeve establish clearance for the sear and loading ramp, as well as reducing friction considerably.
At this point, the bolt is reversed in the chuck (preferably a four-jaw one) and centered using a dial indicator. You can now proceed to drill and bore the inside to the dimensions shown. You will need to add extensions to some of the drills. Drill the holes as deep as possible, using new, sharp drills before using the extended ones. With luck and all possible care, this hole will meet and center on the small hole started from the other end.
A slot must be milled, as shown, to provide clearance for the sear, and the locking lugs must be machined to mate with the lugs in the barrel extension.
With the barrel in place and the bolt in a forward position, ready to close but unlocked, the bolt handle position is scribed through the opening in the receiver slot. The bolt is removed from the receiver, and the handle is welded in place. This should be made up slightly oversized and fitted by removing material to the point that the bolt works freely. That is, it opens and closes and moves forward and back without effort.
The extractor should be machined and installed in the upper right-hand bolt lug. When the bolt is opened, this pulls the empty case to a point where a finger can be hooked over the mouth of the empty case and the case pulled free. No ejector is used in this design since, as a single shot, it is desirable to save the empty case for further use with as little deformation as possible.
The cocking cam is located and marked through the receiver slot and cut as shown. As in other instances, this should be fitted during construction and assembly and may not conform exactly to the dimensions shown.
The firing pin is turned from 1/2-inch (.50-inch) material. This is best done in three stages: (1) forming the front portion, (2) reversing the pin and turning the rear section to size, and (3) threading the rear section,.with the front portion formed first.
The bushing, which holds the firing pin in place is made as shown. The cocking piece also is made from 2 1 /4-inch-diameter material (2.250-inch-diameter) and, again, fitted as assembled.
A hole is drilled through both the bolt body and the firing pin bushing to hold the assembly in place. This should be done in one operation, with the parts assembled and in place. The entire assembly is now fitted and polished until smooth operation is achieved.
The three bolt-lug openings are laid out on the face of the bolt, an equal distance apart, using a dividing head or spacer of some sort, if neither of the latter is available, this spacing can be accomplished by wrapping a piece of masking tape around the diameter and marking the exact diameter on the tape, which is then removed and marked off in three parts. It is then again wrapped around the bolt, whereby each line becomes the centerline of each lug. The openings can now be cut, 1/2-inch wide and 1/4-inch deep, using a 1 /4-inch end mill. The radiused corners can be made square, if desired, with the use of a small square file.
No attempt should be made to chamber the barrel until both the bolt and barrel extension are finished.
The barrel-retaining nut is a straightforward lathe job. It is threaded inside to match the barrel threads. The outside is turned to the same diameter as the receiver tube, and one end is turned to just fit inside the tube.
UPPER RIGHT BOLT LUG, FROM FRONT
* .620" p
.187" SPRNG POCKET
.187" SPRNG POCKET
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