Thread: any Ar15/M4 fans siting around.

Originally Posted by Devilpup

5.56 is actually a little bigger. You can notice when you groups go to heck with just switching from 5.56 round to .223 in a 5.56 barrel. The bullet will actually wobble on a very small scale. I've only seen this with my uncle's 5.56 but they say it common on some of the gun forums.

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Devilpup

No sir, both are .224", I have some military stuff and a lot of my own loads and they are the same diameter...I checked.

The reason a bullet "wobbles" is due to having too slow of a twist rate for a particular bullet. It's called "key-holing". Most rifles can handle a 62gr bullet before loosing accuracy.

Twist rate info:
Barrel Twist Rate 1:14" 1:12" 1:9" 1:8" 1:7" or 1:6.5"
Max Bullet Weight 55gr FB 65gr FB 73gr BT 80gr BT 90gr BT VLD

Also, if you have a Rock River or Armalite AR, you can safely shoot both cartridges as they are designed to be used by our Military or Police off the shelf. They are the only two mfg's that I know of that were designed to shoot either or both rounds. Of course you would have to change some internals and the bolt if you were to need 3-shot or full auto.

Hope this helps to clarify things...
Scott