Details of construction of steel lapping rod, to hold lead laps cast upon it. A is special head for lead laps. B is special head equipped with leather washers, used in burnishing rifle bores to a high polish. C shows ball bearing lapping rod handle made from a bicycle pedal.
tap this size and in attaching this nipple to the pedal shaft you can sweat it on so that it will not unscrew. Clean the threads well and use a good soldering flux on both sets of threads. £et the nipple, upright in a vise or hold it in a pair 6i pliers and heat it so that the solder flowrs readily. • Put the solder in the nipple and continue the heat for a minute then dump the excess solder and screw the pedal shaft in while again applying the heat. After it has cooled drill a hole in the opposite end of the nipple to insert the lapping rod. This may be threaded into the hole and pinned with a straight pin to prevent it unscrewing. The last three inches at the outer end of the rod are squared and nicked on the corners as was done with the rod on which the babbitt rifling head was cast. Two pieces of wood bolted together on opposite sides of the pedal in a right-angle position to the rod will supply a handle. The rod is wrapped with tow or string below the squared portion and inserted in the barrel from the breech and the tip brought just level with the muzzle. Melted lead is used for this lap casting and the barrel should be heated for the last 3", as it was in pouring the babbitt rifling head, so that the shrink of the lead cast will be held at a minimum. After the cast has cooled, gently push it from the muzzle and carefully examine muzzle end of the cast and measure it at the end to see whether the rifling cutter or the land cutter has bell-mouthed the muzzle of the barrel. This is the usual case and as the length of barrel in this condition will be short the barrel will have to be cut off slightly and the muzzle refinished, but do not do this until after the lapping is completed.
In making this examination and measurement of the lap do not push more than 1" of it out of the muzzle, as the lap should never be entirely removed from the barrel or it will be necessary to cast a new lap upon the rod. Use a sharp pocket knife to cut down the expanded portion of the lap at the end so that it will slide freely down the barrel or in casting the lap you can stop the rod about 1" short of the muzzle and the expanded (portion of the lap at the muzzle end can then be cut off with a fine-tooth hacksaw and the burr left on the end by the saw cut off with a knife.
Flour of emery is mixed with sperm-oil or olive-oil to a sirupy mixture and, with the lap withdrawn to the breech end of the barrel, apply the lapping compound to the bore with an undersize bristle brush on a cleaning rod. A .25 caliber brush is right for the .30 caliber barrel. Push the lap well up the barrel and pour a little of the mixture into the breech end and then turn the barrel muzzle-up and allow the mixture to drain out. Push the lap about 1J4" out of the muzzle and apply some of the mixture to the lap with a small brush like a glue brush. Mark the rod so that when the lap is just even with the muzzle, the mark can easily be seen on the upper surface of the rod at the breech, just even with the rear end of the barrel. Withdraw the lap to the rear and make another mark upon the rod when the rear end of the lap is just entering the neck of the chamber. Watch these marks closely while lapping the barrel so that the lap does not pass out of the bore at either end of the barrel.
Push and pull the lap back and forth through the barrel and if any tight spots are noticed, make three or four short strokes back and forth at these points. After lapping for about ten minutes, push the lap an inch or more out of the muzzle and apply fresh lapping mixture with the brush. The lap may be withdrawn part way into the chamber and some lapping compound applied to it at this end with a smaller brush, such as a small camel-hair brush or a, pipe cleaner. Reapply the lapping compound each yten or fifteen minutes for about an hour then apply only sperm-oil or olivc-oil to the lap and lap for about fifteen minutes to a half hour more. This should leave the bore pretty smooth but if it still lacks a polish to suit you the barrel should be carefully cleaned and washed out with gasoline, a new lap cast upon the rod and the barrel lapped for another hour with crocus powder and olive-oil.
We now have the bore finished and can cut off the enlarged muzzle portion, usually half an inch or less, and refinish the muzzle. This may necessitate moving the front sight farther back on the barrel. Remove locking pins in the sight band if any are present, extend the key slot back with a small milling cutter or drill and file it out and make a new key and drive the sight band back to its new position. If the band is too tight to drive back readily, peen it all around with a Stanley composition-face hammer, which will not mar it but will loosen it sufficiently so that it can be driven to its new position. If the key for the front sight band is integral with the barrel a slot may be cut behind it and a key inserted.
We now must enlarge the neck of the chamber, as the larger bullet has cut down the neck clearance so that probably the loaded case will not enter the chamber fully, We make a neck reamer from an 1%2// straight hand reamer by grinding a pilot 1" long on the front end to ride on the lands of the barrel. The teeth behind the pilot are ground to a 45-degree angle with the center line of the reamer, on their ends leading down to the pilot; clearance is ground or stoned on these beveled ends of the teeth and the teeth are honed on their cutting edges to a slight taper, .002" in the length of the chamber neck. Plenty of cutting oil is used on the reamer, which is operated by hand, and it is not forced, the weight of the reamer and reamer wrench supplying the feed. This will cut a fairly tight chamber-neck and if it is tight enough to show signs of high pressure on the fired cases, it may be lapped by drilling out the primer pocket of a fired case and threading the case for a steel rod screwed into the hole. Flour of emery or fine carborundum powder is mixed with sperm or olive-oil to make the lapping compound and this is applied sparingly to the neck of the case and a tap wrench is placed upon the end of the steel rod so that the case may be revolved back and forth. Only a few turns can be made at a time and then new lapping compound must be applied. Clean the chamber and the case thoroughly each time to prevent the lapping compound getting to work on the shoulder of the chamber.
Others calibcrs may be recut as has been described for the .30*06 and in choosing reamers, or making them to enlarge the neck portion of the chamber, allow a minimum clearance over the diameter of the neck of the loaded case of .003" and a maximum clearance of .005". A 1%4// will hone down nicely to handle the .25 calibers enlarged by using the .256" diameter bullets. In connection with this job do not get reckless and try to use 130 grain and heavier bullets, as these are too long to be handled by the ordinary .25 caliber rifling twist. Limit your bullets in this caliber to the 100 grain, or if these are too expensive make a swage and increase the diameter of the cheaper .25 caliber bullets to .256".
The neck clearance of the .270 Winchester enlarged by using the 7 m/m bullet is taken care of by an 8 m/m reamer. The 139 grain 7 m/m bullet will work nicely here.
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