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GUNS Magazine December 2010 - Page 10

• JOHN BARSNESS • Doing it well can boost accuracy. he directions for most rifle-sizing dies are pretty much the same: T Screw the die into the press until it contacts the shellholder, then lube a case and run it into the die. This does result in a case that will probably (though not necessarily) fit your rifle’s chamber, but for really good handloads there’s a little more involved. In some rifles this may size the case too much, leaving a little slop between case and chamber. This results in erratic ignition and cases that stretch during firing. Instead, back the die off a 1/4-turn from contacting the shellholder, and size a fired case. If it won’t go into the chamber easily, turn the die in slightly more and size the case again. Eventually the sized case will just fit the chamber. Resized cases also may or may not be very straight. Ammo loaded with crooked cases normally doesn’t shoot very well, because the bullet isn’t aligned with the bore. The big problem with typical sizing dies is the expander ball. Almost any sizing die, even the cheapest on the market, will size a case very straightly if the expander ball/decapping rod is removed. When the case neck is pulled back over the expander ball, however, the neck is often pulled out of alignment with the case body. It’s hard to seat a bullet so it’s aligned with the case body when the neck is tilted slightly, like a RESiziNG RiFlE CASES miniature Tower of Pisa. Unlike the tilting of the Tower of Pisa, however, case-neck tilting isn’t usually visible to the naked eye. The only way to tell if the expander ball is pulling case necks crooked is to use an alignment gauge such as the RCBS Casemaster. Place the rod of the dial gauge just behind the case mouth and spin the case. If there’s more than .002" variation as you spin the gauge, your case necks are being bent slightly by the expander ball. The first step in solving the problem is understanding the cause. Expander balls are used because case necks vary in diameter, particularly between manufacturers. When resized, the inside diameter of the case mouth varies slightly, creating variations in the neck’s tension on the bullet, usually called “bullet pull.” These variations can cause inaccuracy. The expander ball bumps up the inside of the case neck to a standard diameter, making bullet pull similar from case to case. theexpanderballisoftentheculpritin crookedcases,butthere’sareasonitexists. Case Necks Now, if the necks of each of our cases had the same wall diameter there would be no need for the expander ball. The case could just be pushed into a die that resized the entire case from base to neck, and the case would be perfectly straight. This is exactly how benchrest shooters resize their brass, because their case necks have been outside-turned so each has precisely the same wall thickness. As a matter of fact, the simple Lee Loader hand tool is very similar to the dies benchrest shooters use, and will size cases very straightly, especially with neck-turned brass. Most of us don’t neck-turn our brass, but there are other ways around the problem. One solution is bushing dies, with interchangeable bushings (small rings of steel) in the neck area of the die. You first measure the neck thickness of several cases of the same understandinghowdiesresizecasesresults inmoreaccurateammunition,particularly criticalforlonger-rangeshootingatsmall targets,whetherpaperorprairiedogs. brand, then select a bushing that resizes the necks to .001" to .002" under bullet diameter. Redding “S” dies are an example. Lee’s collet dies perform the same job by pressing the case neck around a mandrel. The advantage of the Lee collet dies is the cases don’t all have to have the same neck thickness. Another solution is to place the expander ball high in the die, just under the neck-sizing area, so the neck is still held in alignment during expansion. In most dies the expander ball is low inside the die, just above the decapping pin, so the neck is expanded when the case is almost out of the die, and unsupported. Forster Benchrest dies use a high expander ball, and also work quite well. Even standard-sizing dies can make very straight cases, right out of the box. I’ve tested many that do— but have also tested many that don’t. With some work, however, most can be modified to size cases straightly. Polishing the expander ball often helps. I do this by removing the expander/ decapper assembly and putting it in an electric drill’s chuck. The assembly can then be spun while holding some medium-fine emery paper around the expander ball. Often the expander ball is slightly out of alignment with the decapping rod. This can be checked by placing the assembly on a Casemaster or other 10 WWW.GUNSMAGAZINE.COM • DECEMBER 2010

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