The .244 Remington was introduced in 1955, 
the same year as it's main competition, the .243 
Winchester.  In the next few years, the .243 
would establish a strong foothold with the 
American public while the .244 would struggle.

    The most-often suggested reason is that 
Winchester wisely provided a 1-in-10" twist for 
the rifling of the .243 barrels, which worked 
with all available bullets.  Remington, 
however, used a 1-in-12" twist for the .244, 
which could not stabilize the heaviest bullets 
(over approximately 90 grains).

    In 1962, Remington re-released the same 
cartridge as the 6mm Remington (there is no 
dimensional difference) but now specifying a 
faster rifling twist to even the field.  Some 
"re-marketing" success has been achieved as the 
6mm Remington has established a significant 
following.