Apples and Oranges? 223 Rem vs 5.56×45 American Eagle


Apples and Oranges? 223 Rem vs 5.56×45 American Eagle

Here’s an odd one. Paul Harrell is taking a look at two varieties of Federal American Eagle ammunition: 223 Rem (AE223J) and 5.56×45 NATO (XM193). Both have 55-grain mull metal jacket boattail (FMJ) bullets, both claim to be “military grade,” and they have similar boxes. So what’s the difference between those two loadings?

No, not the difference between 223 and 5.56 NATO cartridges. That’s something else entirely.

The first difference I noticed when comparing the two loads on Federal’s website is the different muzzle velocity specs: 3165 FPS for the 5.56 and 3240 for the 223.

For folks who claim 5.56 is always hotter, this may come as a shocker. And it leaves one to wonder, “Why?”¬†We don’t really get an answer.

Paul reads the following note from the 223 box: “Mil-spec primer. For best performance use in AR-style firearms.” The 5.56 box says, “Only fire 5.56x45mm ammunition in chambers designed for 5.56x45mm ammunition.”

When it comes to physical differences between these two loadings, there definitely are some. The 5.56’s OAL (overall length) is a bit longer than the 223 and shows discoloration from having been annealed towards the neck/shoulder area, while the 223 is bright shiny brass color throughout.

He can’t describe the other difference other than to say the recess near the rim on the case head looks slightly different.

So there are definite differences, but how will that affect performance? He begins testing that with a chronograph.

5.56 produced these velocities:

  • 3196
  • 3186
  • 3192
  • 3230
  • 3166
  • 3158
  • 3179
  • 3161

That’s an average of 3183.5, which is reasonably close to the advertised 3165 FPS

223 velocities:

  • 3064 (later tossed out)
  • 3064
  • 3103
  • 3041
  • 3066
  • 3085
  • 3056
  • 3087
  • 3045
  • 3059

This produced an average of 3067 FPS, far below the advertised 3240.

(Paul provided no explanation of why he fired 8 rounds of 5.56 and 10 rounds of 223.)

It’s surprising that the 223 is slower than the 5.56, given the factory’s advertised velocities.

Paul goes on to check accuracy, which is far more subjective than velocity. But it serves to compare accuracy in a rifle chambered for 5.56×45; some claim that 223 ammo won’t be accurate when fired from a rifle chambered for 5.56×45 due to chamber size variations.

He demonstrates that to be hogwash.

He weighed some cases to determine whether Federal uses thicker cases for 5.56 and 223, and determined they weigh the same. (Apparently he’s never heard of comparing case capacity by weighing how much water each can hold… maybe next time.)

Hope you enjoy the video.

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Editor & Contributing Writer Russ Chastain is a lifelong hunter and shooter who has spent his life learning about hunting, shooting, guns, ammunition, gunsmithing, reloading, and bullet casting. He started toting his own gun in the woods at age nine and he's pursued deer with rifles since 1982, so his hunting knowledge has been growing for more than three and a half decades. His desire and ability to share this knowledge with others has also grown, and Russ has been professionally writing and editing original hunting & shooting content since 1998. Russ Chastain has a passion for sharing accurate, honest, interesting hunting & shooting knowledge and stories with people of all skill levels.

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