American Handgunner May/June 1978

ITA LOOK AT FULL-LENGTH SIZINGBy DAN COTTERMANshould be noted by all who reloadhandgun cartridges-especially themagnum types-that resizing dies are machinedinternally so as to introduce asmall amount of taper in the body of theresized case. The result is a case dimensionthat is slightly larger near the head orweb area than at the mouth. The taper isintentional, not accidental, because if thedie were machined so as to reduce thecase to a maximum amount for its fulllength it would tend to rest on the bottomof the chamber and bulge irregularlywhen fired. Also worth noting is the factthat, in the event just cited, the bulletwould not be positioned in correct alignmentwith the forcing cone in the chamberwith the result that more bullet upsetwould occur to detract from accuracy.Another unfavorable feature of resizingstraight-sided cases to the same overalldiameter lies in the web area's resistanceto diameter reduction. If, considering theforegoing, a case were to be resized withouttaper, a bulge would appear at thejunction of the wall and the web.If you have a resizing die that does notproduce a slight taper in magnum revolverhulls it is a good idea to resize nomore than a distance that is equal to thedepth to which you intend to seat the bullet.An exception will be found in reloadingfor a revolver cylinder whose chambersvary in diameter. In this instance fulllengthresizing to minimum chamber dimensionswill be necessary.Though not a particularly strong concernwith straight (though not parallel)walled cases, the matter of concentricityof the reloaded cartridge becomes importantwhen we consider so-called bottleneckedtypes. These are, almost withoutexception, handloaded for an ever increasingnumber of single-shot handguns. which is well represented in theThompson/Center Contender series aswell as Remington's XP-100 and numerouscustom creations.Bottle-necked or shouldered ammospills over into handloading for autoloadersand revolvers, too. However, concentricityis of more critical importancewith some of the longer rounds used in thesingle shots where the likes of the .222Remington, .25-35 Winchester, .30-30Winchester and others mav be customloaded for long-range performance.Unfortunately, a number of handloadershave the wrong idea-or no idea atall-about the concentricity of loaded car-tridges and how it should be checked. Weare indebted to Fred Huntington ofOmark-RCBS for information regardingconcentricity and experiments. The methodsof manufacture used by RCBS andother makers of quality reloading dies issuch as to render eccentricity in the neckof full-length resizing dies extremely unlikely;however, RCBS undertook testingof both factory and handloaded ammo inorder to determine relative degrees of eccentricity.The results are fascinating andrevealing.The ammunition was placed on a precisionsurface plate in a V-block. Then, usinga dial indicator sensitive to l/10,000thof an inch, an average bullet misalignmentof 2'/2/10,000 (.0025-inch) was discoveredto exist in a sample of fortyrounds in two different calibers. To balancethe test, a set of full-length resizingdies was taken from stock, a cast beingmade for a preliminary concentricitycheck. The results indicated less eccentricitythan was found in the samples offactory ammunition. However, when thesame dies were used to handload a testsample of empty cases, the same .0025-inch average eccentricity was noted.The fact that ammunition may showsome tiny eccentricity of bullet alignmentmay be attributed to such factors as brass"memory" or spring-back and possibly toa lack of concentricity in case neck wallthickness. The handloading tool manufactureraccepts the responsibility for makingfull-length resizing dies as accurately asmachining techniques will allow and generallymeets the r ponsibility admirably.feThe manufactur r cannot, however, takethe blame for a lack of uniformity in cartridgecases.Other significant anomalies may presentdifficulties. A loaded round will lie atthe bottom of the chamber and, whenfired, will expand upward. Since its centeraxis was not in line with the axis of thechamber, it will take on a shape that is not(Continued on page 64)No. 345 Championship Rip"The practical rip for the practical pistol shooter"P.O. Box 446 * Arcadia * Ca. 91006