.243 Winchester

The .243 Winchester is a .308 Winchester necked down to take a 6.17 mm bullet, and it went on sale in 1955 — three years after its parent — in the Winchester Model 70 and Model 88. It began as a wildcat worked up by the Field and Stream editor Warren Page, who started necking the .308 down as soon as that case existed; Winchester turned it into a factory round after his write-ups had already made the case for it.

The dimensions are the parent’s, almost unchanged. The head is 11.96 mm, the same rim and the same bolt face, so a short action needs only a barrel; the case is 51.94 mm rather than 51.18 mm, because pushing the shoulder forward while necking down buys back a little of the capacity the smaller mouth loses. What made the round unusual in 1955 was not the case but the pair of factory loads Winchester shipped with it: a light bullet for varmints and a 100-grain one for deer-sized game, out of one rifle. Nothing else in the catalogue was being sold that way.

The barrel is what decided its fate against the competition. Remington launched the .244 in the same year, on a different parent case with slightly more capacity, but rifled for lighter bullets; Winchester rifled the .243 one turn in ten inches, fast enough to stabilise a 100-grain bullet, and that single choice is the difference between a cartridge still in every catalogue and one that had to be relaunched under a new name as the 6mm Remington. Shooters wanting bullets heavier than 100 grains today generally need one turn in eight or seven, which is a barrel decision rather than a cartridge one.

Gaps on this page: three of the five rows in the encyclopedia’s ballistics table are recorded here, one for each bullet-weight class it covers; the table states a single 24-inch test barrel and names Barnes, Federal and Hornady factory specifications together with a shooting website, without saying which row came from which, so all three are attributed to the article rather than to a manufacturer. No ballistic coefficient is published beside any of them. The C.I.P. figures transcribed here are the European maxima; SAAMI’s 60,000 psi ceiling is measured differently and is noted rather than stored.