Rimfire (WMR), a substantially more power-ful rimfire round. More powder in the case andheavier bullets equated more power and reachin the field. Recently, the .22 WMR case wasnecked down to take a .17 caliber bullet, andthe 17 Hornady Magnum Rimfire (HMR) wasborn. Since the parent case was based on the.22 WMR, gun manufacturers had only tochange the barrel of any rifle currently beingoffered in .22 WMR to make the .17 HMR.The case length remained the same, as well asthe rim diameter and thickness. In reality, it’s abit more complicated than a simple barrelswap, but it does follow the idea of refining thewheel rather than reinventing it.

The shape and size of the case is often determined by the intended use of the round. Thestandard .22lr case is nominally 0.613 in length and is used for all match ammunition and thebulk of sporting ammunition. There are a few slight variations on this case, the first being thelonger case used on the CCI Stinger, which measures approximately 0.702. The longer

Stinger case is a criticalpart to that round’s highvelocity design by allowingmore powder inside the casewhile still firmly crimpingits 30-grain bullet. AguilaSSS is a move in the otherdirection by using a shortercase, with a length of 0.396.This case was used in con-junction with a 60-grainlubricated lead bulletdesigned to travel at a sub-sonic velocity. Less powdervolume is needed for thisvelocity level, allowing themanufacturer to use ashorter case and longer 60-grain bullet, yet still main-tain the same overalllength as the typical .22lrround.

Another case design inthe rimfire world can befound among the piles of.22lr brass at just about anypublic range. At firstglance, these casings looklike stretched Long Riflecases, and for the most partthat’s what they are. Yearsago, Winchester decided tochange the original .22lrcase by lengthening it toaccommodate more pow-der and a heavier bullet,and in the process createdthe Winchester Magnum

LLooaaddeedd RRoouunndd CCoommppoonneennttssBroken down into the four major components, the .22lr round isdeceptively complex even thought the various components appear tobe simple. This round is a Winchester X-Pert high-velocity hollow-point.

UUnniiqquuee CCaasseessFrom left to right, CCI Stinger, Federal Standard Velocity, AguilaSSS. While all these rounds are classified as .22 Long Rifle, youcan see the great difference in the case and bullet designs.

EEvvoolluuttiioonn ooff RRiimmffiirreeThe natural evolution ofthe .22lr has been long inthe making and this tinyround had seen some dra-matic changes over its lifet ime. Even looking backjust a few years, you can seehow the CCI Stinger roundwas the natural evolutionof the standard velocitycopper plated round byoffering much more velocityand energy. From theStinger, a huge leap for-ward has taken place withthe advent of the necked down case and .17 caliber bullets (CCI Mach 2). The longer CCIStinger case also served as the platform to launch the new .17 Mach 2 rimfire round, the latestevolution in the rimfire world. The Stinger case was modified by necking the case mouth downto .17 caliber, and designing in a rounded bottle-neck case shoulder, similar to that found oncenterfire rounds. This case length was selected because the longer length not only offered themaximum amount of case capacity for powder and neck length for bullet gripping, but the littleextra case length helped the rounds feed reliably in magazine-fed rifles.

WWMMRR aanndd HHMMRR MMaaggnnuumm RRoouunnddssOn the left is the original .22 WMR case design,and on the right is the new .17 caliber bottle-neckcase design. Unlike most centerfire bottle-neckcases, the new .17 HMR uses the traditional rimon the case for headspace orientation.

D e s i g n / R i f l e m a n ’ s G u i d e t o R i m f i r e A m m u n i t i o nS t e v e n B o e l t e r / R i f l e m a n ’ s G u i d e t o R i m f i r e A m m u n i t i o n

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