I posted about these a while back inquiring why the 223 shows a higher velocity (3240) than the 556 (3165) and whether one was actually more powerful than the other.

I didn't get an answer as to which is more powerful, but the common explanation for the 556 being slower was that the 223 is fired from a long barrel bolt action vs. a shorter auto for the 556.

Federal didn't answer my email asking about the differences.

I took one of each apart to see what the differences were.

Primers--both are mil spec and look the same, both are crimped.

Kinetic puller--It took 7 hits to pop the 223 and 10.5 hits for the 556; I'm calling it 10.5 because one of the 11 hits was a bit off.

The cases--556 was 95.9 gr.  223 was 95.7.  Guessing that's just manufacturing variance plus the 556 has sealant at the neck.  They look the same other than headstamp and visible annealing on the 556.

The bullets--556 was 54.8 gr.  223 was 55.2.  Might be some manufacturing variance, but they are different bullets.  The 556 has the cannelure lower for longer seating and the ogive is fatter closer to the tip, more bulbous than the 223.

Powder load--The 556 had 27 gr., the 223 was a calculated 24.8.  I had to calculate the .223 based on component weights subtracted from the complete cartridge weight because powder was spilled during the pulling.  I don't think any 556 powder was lost.

OAL--556 is 2.25  223 is 2.20

At over 2 grains extra powder I now know which is more powerful, both powders look to be the same.

I've shot quite a bit of the 556 and will be shooting some of the 223 soon.

The 223 averages $1 less per 20 box.

Was this the Federal American Eagle AR5.56 designated XM193?

Vince

I think so.  I won't be around the boxes for a few days and I can recheck then.

Most .223 test barrels are 24" long while the test barrel for 5.56 NATO is usually 20".

Yes it is.  I got a chance to try some of the .223 version and it wouldn't cycle my rifle, typical for it with any less than 5.56 power levels.

Why don't you just chrono each from the same barrel?

 

I don't have a chrono yet.

Besides, the speed is meaningless, the ammo that functions is what matters most.

I found PPU 223 runs pretty well as long as the gun's clean and wet, but others are hit & miss.

556 cycles perfectly.

Hand loads at the low end of 556 were also hit & miss so I'm going hotter next round.

I've shot both with no problems.

A coupl'a things:

ONE - Velocity - is that corrected muzzle velocity, instrument velocity at 78 feet or instrument velocity at some other range?  What barrel was the velocity tested in?  The mil-spec for M193 Ball is 3165 fps at 78 feet (+/- 40 fps, with a sigma of 40 fps), from a standard M16 barrel (20" with gas port).  That should be around 3300 fps at the muzzle.


TWO - All ball powder looks pretty much the same, but the burn characteristics can be quite different. Further, between lots the burn characteristics of the same type of powder can be different.  This is why each lot of powder has to have its own load worked up so the velocity is consistent.  In fact the spec sheet from TM 43-0001-27 lists a charge weight with a allowable variation of 2 grains (as required to achieve the velocity requirement.

If you zero with the "556", then shot the "223" does the average point of impact change more than 2 inches?  Does it move up or down?

Without clocking the velocity, you haven't learned much, other than the the two bullets may, or may not be the same shape (by the drawing, the ogive can be from 5.25 to 5.5, and there can be a 0.01 inch variation in the location of the cannelure).

+1 on this

I use both in 5 different ARs w/o any issues.