In 1964, Remington announced the 6mm Remington as a re-envisioned replacement for its circa 1955, 244. Remington had imagined the 244 as a varmint-only round and used a 12-twist barrel that could give better accuracy with the 75- and 90-grain bullets available at that time, compared to a faster twist that would stabilize 100-grain bullets, as Winchester had used in its 243. In the 1950s, limited concentricity of bullet jackets limited accuracy. Providing twist-rate was sufficient to stabilize the bullet, the faster the twist, the lower the accuracy. This is no longer an issue because the best modern bullets have sufficiently concentric jackets to eliminate this problem. Because few shooters could justify buying a 244 Remington that was good only for varminting, when they could buy a ballistically similar 243 Winchester and have a duel-purpose gun, the 244 languished while the 243 thrived. So, in 1964, ten years after introduction of the 244, Remington renamed it, increased SAAMI Specification maximum-working chamber pressure, and changed the rifling-twist so it could offer ammo loaded with 100-grain big-game bullets. They at first called it the 6mm Remington Magnum, which considering the performance of this round, compared to the only other 6mm round on the market, was perfectly logical but, made no sense to many gun-writers. Backlash from the gun press was so harsh Remington stamped over the Magnum marking on all barrels and rifles still in inventory. Only a few got out with the Magnum marking intact. My friend, Pat Ryan, has one of those. While the 243 Winchester has a well-earned reputation among professional ballisticians for generating unexpected pressure spikes and — due entirely to the much-shorter case neck — limited barrel life, the 6mm Remington has exactly the opposite reputation. It never generates anything unexpected during load development testing and barrel life is about twice the barrel life of the 243 Winchester. Despite this, and Remington’s belated improvements and renaming, the 243 remained wildly popular while the (superior in every way) 6mm remained a dismal failure and Remington gave up on it many years ago. Marketing matters! Heritage of this case dates to the 1870s with the introduction of the 40-70 Ballard case.