I have a new Smith and Wesson MP 15 piston operated variation. set up for 556 NATO. I called turners and asked if I can use different ammo in rifle and was told I can use all three ammo's, 556 NATO, 556-45, 223. Has anyone come across this problem? If I can use 223 it would be a lot cheaper. Thanks AL

I'm not familiar with 5.56-45, however......

Guns chambered in 5.56 can shoot EITHER 5.56 or .223 - BUT NOT THE OTHER WAY AROUND. A gun chambered in .223 should only shoot .223.

OR

You can shoot 5.56mm which is the exact same as 5.56mm x 45mm, along with .223 Remington.

If you had a rifle chambered in .223 you could not safely shoot 5.56.

5.56 x 45mm (a.k.a. 5.56 NATO)

.223 Remington

Keep in mind while these cartridges have similar external dimensions, there are construction and loading differences that generate more pressure. 5.56 produces higher pressures than .223 Remington.

5.56 marked barrel: Good for 5.56 NATO and .223 Remington. Generally 5.56 chambered barrels have less potential for accuracy than a .223 chambered barrel. The difference is inconsequential for the majority of us who plink away.

.223 marked barrel: Good for .223 Remington Only. Provides better potential for accuracy over a 5.56 chambered barrel, but can not withstand the pressures generated by the 5.56 cartridge.

.223 Wylde marked barrel: Good for both 5.56 and .223. Created by Bill Wylde to yield the accuracy potential of the .223 chamber while being able to withstand the pressures generated by the 5.56 cartridge.

We could go deeper into the weeds about case wall thickness, primer differences, and differences in chamber leade...

__________________
-John

Thanks for your reply , helped a lot. Al

White Oak Armory has their own .223 chambering as well. Similar to .223 Wylde.

I have an M&P-15 chambered for .223. Is it the case that the only thing I need change is the barrel in order to shoot 5.56?

Are you sure? Look at the barrel and see what is stamped on there. If yours is truly chambered for .223 from factory, you have a rifle that was produced to sell in the international markets.

Oh. My.
All this time I thought it was only .223. Thanks!

.223 is always cheaper, If you are chambered in 5.56 you are GTG.