5.56 or .223 Question

[SendItDownrange]

Got a question. I'm a noob to this forum, so point me in the right direction if this has already been asked and answered. Recently bought a S&W M&P15 chambered in 5.56. The purchase came with 400 rnds. of American Eagle 55gr .223. I've read some things online that suggest running .223 through 5.56 barrel will result in poor accuracy, and running 5.56 through a .223 barrel could result in malfunctions. Myth or Fact?

 

[Mr_MagicMallyMall]

The 5.56 will run a little hotter than the .223, but the difference in accuracy will be little to none. I run 75 gr .223 through my 1:7 (that's the twist rate) 5.56 all the time and have no issues. True though about the malfunctions with 5.56 through .223. Just remember the whole "square (.223) is always a rectangle (5.56), but a rectangle (5.56) isn't always a square (.223)" saying and you'll be good.

 

[Sniper Uncle]

You did well to buy a 5.56, as you can use any .223 ammo available in it. The problem comes when you try to go the other way, as Magic says. You could damage a .223 by shooting 5.56 through it, as you could be over-pressuring it. The 5.56 is made to handle the pressure, so you are safe there.
I think you will like that rifle---I bought one for my wife, and it shoots very nicely. She loves it. I kinda wish I'd gotten one for myself too.

 

[Jhnmdahl]

This page has a reasonably good summary:

http://www.thegunzone.com/556v223.html

John

 

[ORD]

AR15.com! This horse has been beaten to death, resurrected and beaten to death again on more occasions than I care to count.