Is .223 brass and 5.56 brass interchangeable?


June 3, 2011, 01:57 AM
A friend and I were talking who has a .223 and it was brought up that 5.56 guns can shoot 5.56 or .223 as they are interchangeable, but not vise versa. So that made me wonder. When reloading, can you use 5.56 brass in place of .223 brass and just load it to .223 specs and shoot it in a gun rated for .223 only, or does it not work this way?

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Friendly, Don't Fire!
June 3, 2011, 02:02 AM
Supposedly, I believe, No, as the case capacities are apparently different. However, for mid-loads I have used a mixture of .223 and 5.56 brass when I was realocing about 2,000 pcs of brass that were given to me.
June 3, 2011, 03:06 AM
It is always best to work up a load when using different componets such as brass and bullets. Start low and work your way up until you reach the accuracy or velocity that you are seeking, or until you max out on the powder charge, or you start seeing pressure signs. In general the 5.56 nato brass is thicker therefore it has less case volume. Your .223 sizer die will size it to 223 specs except for the case length and it can be used in a 223 rifle if full length resized. Its just the powder charge that has to be adjusted.

June 3, 2011, 06:21 AM
well, the two will fit both rifles, but your powder charge will probably have to be different between the two. military brass is thicker, leaving less room inside the case, which with the same powder charge, will give higher pressures. pressure is a double edged sword. you have to have it, or the bullet will go nowhere, but to much will cause catastrophic results. seperate your brass, and work up loads for both, or get rid of one or the other, and stick with it.

June 3, 2011, 07:20 AM
It's best to weigh the brass, there is a lot of variance between mfg's.

June 3, 2011, 07:45 AM
SOME military brass is thicker. But thicker than what is the question. The heaviest brass out there is Lapua commercial .223 brass. The lightest with the highest capacity is Lake City mil brass. Point being that you can't make a blanket statement about the difference between 5.56 and .223 brass like you can with 7.62x51 and .308 brass. In the former case the only difference in the chambers is the leade and heavier brass is not needed. In the latter case, the .308 falls within the tolerance range of the 7.62 but the 7.62 is spec'd with a very "roomy" chamber to increase chambering reliability. 7.62 brass is loaded to a lower pressure in thicker brass to keep from rupturing cases in the "oversized" military chamber.

With .223/5.56, the brass is 100% interchangeable. The difference is the spec to which factory ammo is loaded. As brass, there is no difference. If you're loading to the ragged edge of the max or looking for the best possible consistency, you would want to sort by headstamp at the very least to keep the small differences in case volume from having an effect. For mid-range blasting ammo, the difference isn't even of note.

June 3, 2011, 11:54 AM
I found the same thing that helotaxi did: Lake City 5.56 brass has more case capacity than commercial brass I have checked.

I run nothing but Lake City brass in my 223.

June 3, 2011, 12:10 PM
.223 Rem different then 5.56 NATO?
Try buying a set of 5.56 NATO reloading dies some time!

And I agree that military 5.56 brass is just as likely to be lighter and have more capacity then it is to be heavier and have less.

From a reloading standpoint, the only differance is, all 5.56 NATO spec brass has crimped primer pockets that have to be reamed or swaged out before you can reload them.

But some .223 commercial is now showing up with crimped primers too.

So, is there a differance?
Most definately!

.223 Rem says .223 Rem on the headstamp, and 5.56 NATO doesn't.
And that's about it!


June 3, 2011, 01:01 PM
I noticed that crimp on the 223 brass these days too. I view it as a negative development. I leave all crimped brass for somebody with a swagger these days. Life's too short to do it by hand and 223 brass is everywhere.

I've found that when I trim my range pickup brass that the 556 lake city brass has a longer neck and requires more trimming, but other than that, it's all pretty much the same.

June 3, 2011, 01:57 PM
With all these differences in cases, you can only judge it on case-by-case basis.

June 4, 2011, 06:54 AM
When reloading you have to keep your eyes open and watch out. It seems just when I think that I have a handle on it all the "experts" crank the handle on me.:p The changes are minute with the brass and the original specs when loaded are the main difference.

June 4, 2011, 08:45 AM
Here are a couple good reads on the subject. Notice, both show that 5.56 brass more case capacity than commercial 223 brass.

OH, I almost forgot, yes, they are interchangeable.

June 4, 2011, 01:42 PM
i've been weighing cases for my accuracy loads for well over 40 years. It is a popular myth that US made 5.56mm cases are thicker than commercial cases. Federal American Eagle and Gold Medal .223 cases are about five grains heavier than LC 5.56mm cases. As the poster mentioned above, Lapua cases are the heaviest cases made. Some Brit made 5.56mm cases are thick.

Go to case weights:

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