Metric Ammunition

[stymie222]

I might buy a tactical rifle in the near future. I have been away from the rifle market for a long time.
Could some one explain the calibers that are now being used and their performance ?

5.56 x 45mm NATO- In relationship to American gauge ammo, what would you compare this to ?

[Fronty Owner]

5.56X45 NATO is .223 Remington... sorta.

the NATO ammo is loaded a bit differently than .223 Remington.
you can fire .223 Remington thru a 5.56X45 chambered rifle, but shouldn't go the other way because of excessive chamber pressures. The lands on the rifling of a 5.56X45 is further than a .223. this give the bullet a bit of free space to move before engaging rifling.