Have a read here mate.

http://www.6mmbr.com/gunweek084.html

It is as simlpe as I like European calibers.
Great brass.
Runs at 63 000 psi
Treads on the heals of the 260
Shorter fatter case allows the projectile to be seated out futher.

As a mates says "you can load it with saw dust and it will shoot".