WARNING:All technical data in this publication, especially for handloading, reflect the limited experience of individuals using specific tools, products, equipment and components under specific conditions and circ*mstances not necessarily reported in the article and over which the National Rifle Association (NRA) has no control. The data has not otherwise been tested or verified by the NRA. The NRA, its agents, officers and employees accept no responsibility for the results obtained by persons using such data and disclaim all liability for any consequential injuries or damages. Above: Neck turning with thisSinclair tool improvesuniformity of bullet pull.
Upon firing a high-pressure rifle cartridge, the case is slammed forward and rearward, expanding against the chamber walls and battered by all manner of shock waves and vibrationscoursing through the barrel, action andstock. The best accuracy is achievedby making the forces acting upon therifle and bullet more uniform, and byminimizing shot-to-shot variations inbullet velocity.Here’s how to do it.
When a modernhigh-intensity rifle cartridge is fired, all manner of shock waves and vibrations course through the barrel, action and stock. Best accuracy is achieved by reducing the randomness of these vibrations, and by minimizing shot-to-shot variations in bullet velocity. To achieve this, most competition rifle shooters rely upon carefully reloaded ammunition.
The initial phase of precision reloading is case preparation—a set of operations designed to produce cases that are as uniform as possible in everyrespect. The following describes thecase preparation process employed forabsolute maximum accuracy. These procedures can be performed on new cases and/or fired cases that havebeen cleaned (tumbled and with necks brushed out).
Sizing
When a cartridge is fired, the brasscase expands against the chamberwalls, and then, when chamber pressuredrops, springs back—but onlypartially. Thus, each fired case must bere-sized in a sizing die to restore it toits original dimensions.
Neck sizing bushing-type “hand dies” from L.E. Wilson are extremely precise using a simple arbor press and accessories.
Magazine-fed rifle brass is commonlyfull-length resized with diesthat reduce the neck and body diameterand push the shoulder back. Suchdies also incorporate a decapping pinthat removes the spent primer, and anexpander ball that opens the neck toa size slightly smaller than bullet diameter.Small-base dies reduce the casebody diameter even more, particularlyin the head area (promoting feedingin semi-autos), while bumpdies slightly move theshoulder back withoutreducingcase diameter.
New cases should berun through a full-lengthsizing die before loading, toreduce body irregularities andto have the expander ball ironout dinged case necks. Casesused in single-shot (and some magazine-fed) bolt-action rifles are oftenonly neck sized. Neck sizing diesreduce neck diameter only,leaving the case bodyunsized for closer alignmentof the case andchamber, potentiallyenhancing accuracy. Neck-sizing bushing diesthat use interchangeable bushings are also popular,available in 0.0005-inch or 0.001-inchincrements, to precisely size theneck for more control over bullet pull(the force needed to move the bulletthrough the neck).
Standard and/or bushing-stylematch-grade sizing dies for 7⁄8-14threaded presses are made by all themajor manufacturers. Alternatively,neck-sizing can be accomplished withthe highly precise L. E. Wilson bushingdies, used with a smallarbor press.
Lubrication is required with sometypes of bushings when cases are tobe full-length sized or neck sized.
Measuring neck wall uniformity
This tool from Sinclair measures neck wall runout for case wall uniformity.
Uniform neck wall thickness isimportant for both a consistent bulletpull, and for ensuring that the neck’sinside diameter is concentric to thechamber and bore. Additionally, neckwall variations normally reflect variancesin case body thickness, whichcan produce asymmetricalcase stretching upon firing.Neck wall thickness can begauged using a conventionalball micrometer, case neckmicrometers from Sinclairand K&M, or special neck gaugingtools from Sinclair and others. Withall these, the case neck is slid over amandrel and readings made using amicrometer or dialindicator as the caseis rotated.
Ideally, for match use,case necks should have nomore than 0.0015-inch of runout. Neckwall thickness across any batch ofcases should also be uniform within0.001- to 0.0015-inches.For accurate readings with thesetools, new cases must have theirmouths deburred and their necksexpanded with the sizing die’s expanderball to give perfectly round necksthat properly fit the tool’s mandrel.
Neck turning
Neck turning involves shaving a minuteamount of brass from the outsideof the case neck to produce uniformneck wall thickness. Neck turning isalso required for custom “tight neck”chambers designed for minimal caseneck clearance. By allowing close bulletalignment with the bore axis, suchchambers promote straight bullet entryinto the rifling, increasing accuracy.In general, case necks in tight-neckchambers should have about 0.002-inch total clearance (e.g., if the neckportion of the chamber measures0.313-inch, the outside diameter of acase neck, with bullet seated, shouldbe 0.311-inch). Some bench resters turntheir necks to within 0.001-inch totalclearance—0.0005-inch per side—about the minimum that allows theneck to expand and release the bullet.
Neck turning tools have a mandrelthat fits inside the neck and anadjustable cutter that removes materialwhen the case is turned. Perhaps thebest such tool is the Sinclair PremiumNeck Turning Tool (lead photo), whichfeatures an ergonomic body andclick adjustments in cutter depth of0.0002- to 0.00025-inch per click, allowingprecise control over neck thickness.Neck-turned cases should be neck sized with bushing dies to adjust necktension for proper bullet pull.
Flash hole deburring
Specialized tools are used to remove burrs from the flash hole inside the case.
Burrs around flash holes can interferewith the primer spark transmittedthrough the hole. Removing theseburrs is done with a flash hole deburrer,essentially a small cutter havingan indexing pin that fits in the flashhole. Flash hole deburrers range fromsimple hand tools to models that cutto a consistent pre-set depth. Flashhole deburring needs to be doneonly once.
Primer pocket uniforming, reaming and cleaning
This primer pocket uniformer cuts the pocket square and to a uniform depth.
For consistent primer ignition, manyreloaders recut the primer pocketssquare to the case head and to auniform depth. This requires a primerpocket uniformer, a hardened steel or carbide cutterattached to a handle or to an adapterfor a cordless screwdriver. Someexperts recommend uniforming primerpockets each time cases are reloaded.Removing the crimp around theprimer of military cases is necessarybefore new primers can be seated,and is accomplished using tools thatswage or ream the primer pocket. Allprimer pockets—uniformed or not,should be cleaned after depriming(removal of the fired primer). This canbe done with a small metal scraper orwire brush.
Case length measuring and trimming
Before loading, all cases should be measured to determine if they need to be trimmed.
Overly-long cases can becomejammed into the case mouth shoulderin the chamber. This prevents the caseneck expansion necessary to properlyrelease the bullet, and increases chamberpressure. All cases should be measuredfor length each time they arereloaded. Those longer than the “trimto” length in reloading manuals—usually0.010-inch less than nominal caselength, should be shortened using acase trimmer. Most trimmers consistof a mandrel that fits inside the casemouth, and a cutter that trims the neckwhen the case or cutter is rotated.
Case mouth deburring and chamfering
Sinclair case mouth deburring tool holder.
For proper case neck alignment,clearance in the chamber and easierbullet seating, it is necessary toremove the raised burr often foundinside and/or outside the mouths ofnew or just-trimmed cases. Casemouth deburring can be performedwith a simple hand tool having insideand outside cutting blades at oppositeends, or with more precise unitsthat give a consistent bevel depth.For seating boattail bullets, SinclairInternational and Wilson both makeinside chamfering tools that cut a shallowerbevel than traditional 45-degreedeburrers.
Motorized case preparation
Case trimming, case mouthdeburring, primer pocket uniformingand cleaning andmore can be speeded-upusing power-driven units such as fromGiraud, Gracey, Hornady and RCBS.Some are single-function tools, whileothers, such as Hornady’s Lock-N-LoadPower Case Prep Center, havemultiple stations for different casepreparation activities.
Case weighing
Cases should be sorted by weight, which can reflect differences in volume.
Weight uniformity among casesof the same brand can indicate casevolume consistency. Cases shouldbe weighed after trimming, primerpocket uniforming, neck turning, anddeburring of the flash hole and casemouth. With the cases thus made asexternally uniform as possible, anyweight differences must reflect variationsin case volume. Precisionshooters normally sort cases intobatches consistent to plus or minus 1/2- to 1-grain.
Case gauging
Body straightness, neck concentricity and other case dimensions can be easured by tools such as this NECO Concentricity, Wall Thickness and Runout Guage.
Case straightness and concentricitycan be gauged using tools from NECO,RCBS and Sinclair. Inthese units, the case is setin V-blocks or ball bearings andis rotated while a dial indicatormeasures the case at differentpoints, revealing a non-concentricneck or a banana-shapedcase body. Such irregularitiesin new cases are often correctedwhen the case is first fired and conformsto the gun’s chamber.
Note that the foregoing is only abrief overview; detailed instructions onthe use of the various case preparationtools should be obtained from eachtool’s manual. Also, only the mostaccurate rifles will benefit from thisfull case prep treatment, and manyhighly successful shooters omit oneor more of the steps described above.For many disciplines, one may arguablyneed only to resize and trim thecases, debur the flash holes and casemouths, and perhaps sort the cases byneck wall uniformity or weight. Doingmuch more than this, some claim,provides little more than psychologicalreassurance. Others swear by a moreinvolved process. The intelligent reloadershould experiment to determinewhich case prep operations produce adifference on target.
All the items mentioned in thisarticleare available from one or more ofthe following:
Brownells, Inc.—www.brownells.com
Creedmoor Sports,Inc.—www.creedmoorsports.com
Midsouth Shooters Supply—www.midsouthshootersupply.com
MidwayUSA—www.midwayusa.com
