6 x 45mm (6mm-223 Remington)

Historical Notes:

The 6mm-223 Remington, also known as the 6x45mm, came into being in late 1965, shortly after Remington introduced the 223 Remington as a sporting round. Various experimenters built rifles for this cartridge (in order to take advantage of the reduced wind drift offered by the 6mm caliber, as opposed to the original 22 caliber bullet) for benchrest or varmint shooting. Jim Stekl, then manager of Remington's custom shop, set an IBS 200 yard Sporter aggregate record of .3069 MOA in 1973 using the 6x45mm. For a time, some owners of AR-15 rifles rebarreled their rifles to this caliber for use in NRA National Match Course competition. However, the 6x45mm can not compete successfully with the 7.62x51mmNATO (308 Winchester) round at ranges beyond 300 yards. After its brief flurry as a benchrest and match cartridge, the 6x45mm has now been relegated primarily a varmint cartridge, used by those who want more power than the 223 with the added advantage of being able to use cheap military brass for forming cases. Reloading dies are available from RCBS and chambering reamers from Clymer.

General Comments:

The 6x45mm is one of a series of 6mm benchrest cartridges based on necking up the 223 Remington and 222 Remington Magnum brass. None have any great advantage over the other, and all are capable of extremely fine accuracy. Probably the only advantage of the 6x45mm is that it is based on the 5.56mm (223 Remington) military case. On the other hand, its shorter permits the use of bullets up to 100 grains in weight to be seated to an overall length that will feed through magazine rifles such as the Colt AR-15, Ruger Mini-14, and Remington 788. In power, the 6x45mm is between the old 25-35 and the 250 Savage, which would make it rather marginal as a deer cartridge except under ideal conditions. It is, however, as close to ideal as a varmint and small game cartridge out to 300 yards. This cartridge has become very popular in the Thompson/Center Contender and Remington XP-100 handguns. Bob Milek, the first editor of Guns & Ammo and Peterson's Hunting magazines shot a custom XP-100 in 6x45mm for a number of years. Rifles chambered for cartridges in this group are pleasant to shoot, have relatively low report and are noted for long barrel life.

Source: Cartridges of the World

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