I have an Ar-15 upper with .223-5.56 stamped on the barrel. Which would be the better ammo to shoot? Have read a few articles on this matter but kinda just confused me more. Some say .223 will not be as accurate because of the larger leade for the 5.56? Some say 5.56 is to hot and will damage your rifle. Any help will be appreciated!

If your barrel is stamped 5.56 it should be fine shooting that caliber. I have shot both out of my Rock River AR and haven't felt much difference between the two.

I'm new to this and don't know the exact reason but someone correct me if I'm wrong. The factoids I've found:

1.) A barrel stamped 5.56 can shoot 5.56 & .223.

2.) A barrel stamped .223 should only shoot .223.

3.) Leade = the distance the projectile has to travel before it contacts the barrel's rifling.

4.) .223 leade is shorter than 5.56.

5.) .223 & 5.56 are practically the same dimensionally. The difference is in the powder charge. Powder Charge 5.56 > Powder Charge .223.

6.) Since a .223 round is designed for a shorter lead, it will be more accurate in a .223 barrel because the projectile contacts the rifling sooner. The "tighter" chamber to leade does not not require as much powder charge in a round of .223 v.s. a 5.56.

7.) A 5.56 round is designed for a longer leade. The "looser" chamber to leade allows for the higher pressures the increased powder charge generates in a 5.56.

I'm really waiting for a more experienced member to chime in. I've read posts where some individuals swear it's ok to shoot 5.56 out of a .223 barrel. Some say it's not a good idea.

As for me, I chose my M&P 15-Sport because it has a 5.56 barrel. That way I know I can safely shoot 5.56 & .223.

1.) Correct
2.) Correct
3.) Almost correct --- the significant dimension is the length of the leade --- different projectiles differing in length, seating depth, etc., may vary in overall length, but the chamber throat is fixed, and this is the critical dimension.
4.) Correct
5.) Not necessarily, and not germane to the discussion --- the issue is chamber dimension and variances in case dimensions...
6.) Maybe, but has nothing to do with charge weight, everything to do with chamber and case dimensions.
7.) No, other way to --- "oversize" 5.56 cartridges may generate unsafe pressures in SAAMI spec .223 chambers, irrespective of powder charges.

Bottom line is this: It's OK to shoot .223 and 5.56mm ammo in barrels chambered and labeled as 5.56, but not the other way to, i.e., don't shoot ammo labeled as 5.56 in .223 chambers, period.

The fact of the matter is that you can, and likely will get excellent accuracy from .223 ammo in 5.56 spec chambers, and that you do risk damage to your gun and yourself by creating excessive pressures by firing 5.56 ammo in .223 chambers. See more about this on the SAAMI (Sporting Arms and Ammunition) website.

You are correct. 556 pressures exceed that of a 223 Remington in the neighborhood of 10,000 psi. As far as the leade, NATO is longer, saami is shorter.

The 556 has more oomph downrange than the more sporty 223, but I find that rifles being as quirky as they are, a particular rifle may group better with one particular bullet over another in design, weight, BC, and in the case of the 556/223 AR, chamberings in general. A weapon that fires two technically different rounds adds to the mayhem of finding that sweet spot between accuracy, power, and downrange trajectory.

I hunt deer with the 223, more bullet styles available in that offering that I find suitable. But, the 556 has a slightly flatter long range trajectory and carries more energy.

As for the hub bub about accuracy differences, try out different weights in each round and you'll see that both the 556 and 223 can be accurate. I've shot 223s in a 1/8 and 1/9 barrel with good results, same for the NATO round with good results on both end of the spectrum, no more or less for either. However, light .22s, like a 45 jhp or 50 gr varmint grenade aren't stabilized that well in a fast twist barrel due to there weight. I've tried em, not really impressive. In my bolt gun however, coyote death!

Thanks guys for the info. I'm still learning and appreciate it.

There's so much to learn.

X 2!

You're welcome guys.

The main difference even after all those facts between the 556 and 223 was the 556 is the military style grade round and the 223 was developed from civilian gun manufactures.

Well, you do have to bear in mind that the .223 is the parent cartridge. There would be no 556 without it's standardization with the military. The Remington was developed in the 50's and adopted as a NATO cartridge in the early 60's. The .223 wasn't even a commercial cartridge till the mid 60's. Both were developed by civvies, but that's all.