5.56 versus .223

[m9fan]

I just bought a new Bushmaster AR-15 that will feed & fire 5.56 and .223 ammunition. When considering price and bullet performance, which is the preferable ammo to be firing from my new weapon?

Thanks, guys!

[highscore]

5.56 is a military chamber, cut larger than the .223. Therefore, .223 fits into the 5.56 but not always the other way around. What ammo to shoot depends on what you want to do with it. Blasting full 30 round mags as fast as you can pull the trigger dictates that you shoot surplus 5.56 ammo, but if real accuracy is your intent, you will have to test various ammo to see what your particular rifle likes. Barrel twist also limits how heavy the bullets can weigh and be shot accurately.
HS

[Ishpeck]

Originally Posted by highscore

5.56 is a military chamber, cut larger than the .223.

I thought they looked the same and it was the pressure that differentiated them.

[KarolinaKid]

Originally Posted by Ishpeck

I thought they looked the same and it was the pressure that differentiated them.

They do indeed "look" the same, but technically they are slightly different in size. And, the .556 does indeed have higher pressure. There is another thread on here somewhere about this that I think someone posted illustrations of the technical specs between the two, or a link to the specs.

[jeepinbanditrider]

The chambers are slightly different and actual 5.56 NATO ammo is loaded to higher pressures.

The differences are small but it's enough of a difference that SAMMI recommends that you don't shoot 5.56 NATO in a .223 chamber.

[rogerxd45]

5.56 will give you some extra FPS so since you gun can shoot it then by all means go for it.
the only problem is its pretty hard to find. the only thing i can find locally is the winchester xm193 i think is what its called but i have a feeling that its loaded to 223 specs. i did shoot a friends 16" ar with m855 and it is more powerful.

[jeepinbanditrider]

Originally Posted by rogerxd45

5.56 will give you some extra FPS so since you gun can shoot it then by all means go for it.
the only problem is its pretty hard to find. the only thing i can find locally is the winchester xm193 i think is what its called but i have a feeling that its loaded to 223 specs. i did shoot a friends 16" ar with m855 and it is more powerful.

XM193 is loaded to M193 5.56NATO specs but packs a 55 grn bullet as opposed to the 62 grain in the M855.

The X in XM193 actually designates it as factory seconds that got rejected because that lot didn't meet NATO ammo specs for M193.

Neither is necessarily more "powerful" than the other. The M855 is spoused to be better at penetrating body armor and helmets at longer range. Some say the M193 ammo works better on unarmored targets.

[m9fan]

Thanks for everyone's input. Does anyone know of retailers that sell 5.56 ammo, or should I just seek it out in bulk at a local gun show?

[AR15Doc]

Originally Posted by m9fan

I just bought a new Bushmaster AR-15 that will feed & fire 5.56 and .223 ammunition. When considering price and bullet performance, which is the preferable ammo to be firing from my new weapon?

Thanks, guys!

The .223 versus 5.56 dilemma has confused people for years and you will hear all kinds of inaccurate beliefs concerning the difference between the two rounds that people have heard and passed down over the years. It never ceases to amaze how many different and skewed claims are floating around out there on this subject.

The fact is, the external dimensions of the .223 and the 5.56 rounds are identical. The only difference in the rounds is in the case wall thickness, which is typically thicker in the 5.56 round and the powder charge, which is larger in the 5.56. Other than that, there is no difference size or shape of the cartridges.

The difference is in the chambering (not the cartridge). The primary difference is that the 5.56 chamber has a longer leade (the distance between the end of the case and the point where the bullet contacts the rifling. There are actually a number of variations on 5.56 chambering that include larger chamber dimensions of one type or another compared to the .223 chamber as well, but the primary difference (and the one that make the pressure difference) is the leade distance.

The longer leade of the 5.56 chamber does not build pressure as sharply as does the shorter .223 leade, therefore, 5.56 ammunition is loaded hotter to make up the difference in pressure loss (plus military spec ammunition is intended to be near max performance for greatest impact and penetration). If you fire a 5.56 round in a .223 chamber the shorter leade will increase the pressure of the round faster than the 5.56 chamber will causing an over pressure of the cartridge (as much as 20,000 PSI more), which is about the proof load pressure for most .223 chambers. This means that every 5.56 round fired in a .223 chamber is in effect a proof load. In short, firing 5.56 ammo in .223 chambers is creates a high risk of chamber failure. Conversely, if you fire .223 in a 5.56 chamber, it will not reach the same pressure as it would normally in a .223 chamber, thus, .223 ammo is weaker in 5.56 chambered weapons. As a result, mild loaded .223 ammo will often fail to cycle a 5.56 weapon.

In short, the only difference in the 5.56 and .223 ammunition is that 5.56 is designed for a more forgiving chamber and .223 is designed for a tighter fitting chamber. The result is higher pressures from the 5.56 ammo. Other than that, there is not difference in external dimensions of the two rounds.

So, why the difference? Military chambers are cut this way to accommodate a wider variation in ammunition construction. While the U.S. military and NATO for that matter have strict tolerances for the manufacture of ammo, it is known that in war time they may need to accept and use ammo made to less stringent tolerances. Likewise, the larger chamber tolerance allows some forgiveness for contaminants introduced with the ammo. The Russian weapons exploit this to a great degree. While accuracy suffers some, function is greatly enhanced.

On the other hand, the .223 chamber is built for accuracy. Shorter leade and tighter chambers mean better alignment of the bullet into the rifling and better performance. In short, the .223 chamber will out perform the 5.56 in terms of accuracy but the 5.56 will provide better functionality in adverse conditions and ammo tolerance.

The goal has been to find that optimum chamber that will span both ends of the spectrum. This is the idea behind the Wylde and Armalite chambers, which sort of split the difference to increase accuracy while sacrificing little in terms of functionality. These chambers can handle both .223 and 5.56 ammo and are more accurate than the standard 5.56 (nearing that of the .223).

So, there you have it in a nutshell (a big nutshell). Now as for your last question in the thread...where to find ammo....I suggest Wideners.com. They have a good selection at the best prices. I also recommend the PRVI Partisan m193 and M855 ammo. It is good stuff. For plinking, the Barnaul .223 55gr FMJ or SP is loaded hot and functions well in AR-15's. While not as accurate, it is great plinking ammo for the price. The Barnaul 55gr FMJ is the same thing as the Monarch blue box at Academy stores.

I hope this helps.

[Tally XD]

Wow! Damn good first post! Welcome to the forum