556 Vs American Eagle 223 Ammo 100 Rounds : How They Differ

There is much debate in the firearms world about the similarity between American Eagle 223 ammo 100 rounds and 556, ammunition that’s created by the same manufacturer. In fact, it’s quite a polarizing argument.

Out there you’ll find one side saying that to use 556 ammo in a rifle with a true 223 chamber is dangerous. They say that you’re likely to damage your gun and yourself by doing this, whereas others say that there’s no discernible difference.

So, who is right? Are there too many variables to consider? That’s what we look at here, as we try them both side by side. Out on our 100 yard range, we put both through their paces. We’ll get to the results shortly, but let’s first look and see if there’s much of a physical difference between the two. 

The Dimension & Weight Differences

When you look at American Eagle 223 Ammo 100 Rounds and the 556 option while they’re still in their boxes, you will notice that one is longer than the other. However, before we get ahead of ourselves, that’s entirely down to the way each variety is packaged.

556 ammo comes with nice neat clips to hold the rounds in place, while the 223s are just loose in the box. It would seem that the manufacturers themselves think there’s a difference!

The Facts About the physical differences…

Physically speaking, both are 55 grain, full metal jacket spearpoint projectiles and the casing length for both is exactly the same. That said, when you put both next to each other, you will notice that the 223s are slightly shorter, by around 2 mm. 

American Eagle 223 Ammo 100 rounds are also different in their coloring, as the casing has a nice yellow brass sheen. Compare that to the 556 that looks quite discolored – which it is, due to being heat treated around the shoulder.

And what about the thicker casing on the 556?…

Some cite the thicker casing on the 556 as one of the main differences, which offers reduced capacity for the propellant, so we decided to weigh the casings on their own. Do you know what you found? Almost identical weights, with just a .08 grain difference. 

If the 556 casings were noticeably thicker, then this would equate to a higher grain, but it doesn’t, perhaps suggesting that it’s something of a myth. 

So What About Performance?

We set up our chronograph and fired both (from a true 223 chamber) and what we found was really interesting. The 556 had a mean velocity of 3,180 ft per second, whereas the 223’s mean velocity was closer to 3,050, showing that there is a difference in speed. 

Shooting both over 100 yards, we found no real difference in accuracy, as the groupings were almost identical. The differences we saw were what you’d expect from shooter error over anything else. 

So, the $64 Million Question – How Different Are They?

Ok, so the American Eagle 223 Ammo 100 rounds is pretty much the same in every regard, aside from a slight difference in speed. The conclusion we can draw from this is that, technically, yes, there are differences as we’ve mentioned.

Do those differences really matter? Perhaps not as much as some claim. Will it destroy your rifle if you use a 556 in a true 223 NATO chamber? That’s not what we found. 

So, there you have it. We’re sure that the claims some have are overblown, as the difference was so small, so next time you hear someone claim the opposite, you can say that you know someone who might not agree with them!

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