What was the MSR first chambered for?

The MSR (Modern Sporting Rifle) was first chambered for the .223 Remington cartridge. This caliber, which is widely used in both civilian and military applications, gained popularity due to its low recoil and flat trajectory, making it suitable for various shooting activities. The MSR platform has since expanded to accommodate a range of calibers, but the .223 Remington remains one of its most iconic chamberings.