Why do some of you choose 5.56 over .223 ammo? It cost more so I'm wondering if it's because of .223 ammo shortage, because you gun can handle it so why not, because Military uses it, more velocity, etc.

Edit: My question is not so much comparing the two specs. My question is, if you were to go to the store and there where two boxes, one .223 and one 5.56, why would you choose the 5.56? So far it seems that you would only purchase 5.56 if .223 was unavailable. I know others out there only buy 5.56 so I'm trying to figure out why? If there is good justification maybe I'll switch over. I'm also going to reload so if that should be factored in too.

.223 is cheaper
.223 can be fired in a .223 and 5.56 barrel

5.56 has slightly higher velocity
5.56 cannot be fired in a .233 only barrel

Price and avaibility.

I have always thought that 5.56 is more expensive than .223.

It's the same projectile so I don't think shortage is an issue.  5.56 is just loaded "hotter" so higher velocity.  The size of the cartridge is slightly different also which is why they say you can fire a 223 in a 556 barrel but it isn't advisable to do the opposite.  It seems most barrels are chambered in 556 so they can shoot both, the exception bring some precision 223 stainless barrels.

That's my understanding anyway. 

My question is not so much comparing the two specs. My question is, if you were to go to the store and there where two boxes, one .223 and one 5.56, why would you choose the 5.56? So far it seems that you would only purchase 5.56 if .223 was unavailable. I know others out there only buy 5.56 so I'm trying to figure out why? If there is good justification maybe I'll switch over. I'm also going to reload so if that should be factored in too.

.223 is cheaper
.223 can be fired in a .223 and 5.56 barrel

5.56 has slightly higher velocity
5.56 cannot be fired in a .233 only barrel

Same price as .223
5.56 is loaded hotter to military spec
Better for all purpose use (range, shtf etc)
Just rather have the full power version of two very similar cartridges

If you reload, 223 is less likely to have crimped primer pockets. ( some 223 manufacturers do crimp their pockets as well) I have both 223 and 556. 556 is stored for shtf scenarios, while I practice and plink with 223 since it takes a step out of the reloading equation.

Because I feel operator shooting mil-spec ammo through my rifles.

JK. Like everyone says, 5.56 is hotter. My AR-15 has heavy buffer and spring, so I don't trust shooting .223 in it. I shot some .223 Tula in my AK and I had a few failure to feed. Maybe it was the brand, but the extra power of the 5.56 makes me feel better.

.223 is the more American round, being standard measurements.

556 has a tendency to crack or explode barrels sooner and cause faster wear on all your moving parts
also its harder to reload because the neck is tempered and the primers are crimped in.
the angle of the shoulder on a 223 and 556 is different. 
556 tending to be hotter is less accurate also will wear out your gun faster.
I try not to shoot 556 because it makes my shoulder hurt.

But if you want maximum bullet head efficiency you will need to use 556 since it is more powerful than the 223 round.

5.56 should run more reliably, because it is hotter.  However, you might sacrifice a bit of accuracy.

My gun runs fine with .223, and that's what I'm sighted in for, however I'll buy whatever is cheaper.

you can get 556 any where in the world its a common round if you was in the jungle with your 223 gun and ran out of ammo but theres lots of 556 all around the jungle on dead bodies you cannot use there ammo with a 556 it fits right in

just like the ar15 if the upper receiver breaks you can take someone elses reciever and attach it to yours very convienient if your in the thick of things

just incase theres zombies go 556

You just need 22LR to zap a Zombie.....Headshot!

Are the 22 shortsge over or srill going on?

Are the 22 shortsge over or srill going on?

pretty much over but prices are still high.

I'll shoot both .223 Rem and 5.56.  If given the choice and about the same price, I'll buy 5.56.  I try to make sure both .223 and 5.56 run in my guns, but I do notice stronger and more consistent ejection with 5.56 in my mid-length gas guns.  I don't really notice a difference in recoil between .223 Rem and 5.56...

I have noticed that my mid-length gas guns do NOT like the weaker Tula .223 Rem.  They will run fine in my carbine gas guns, but the mid-lengths guns to not like Tula. 

My guns are also zeroed for 5.56.  My ARs aren't precision guns, so that's not a big deal for me. 

I shoot 5.56 because OGC or SEC always have deals on it in bulk.
And that's what I'm zero'd for.  ( 55grainers )

However, out of my MVP bolt gun ( 5.56 chamber ) I shoot mostly .223 because I shoot 62 grain SPs and there's a lot of hunting rounds available in 223.
( and I don't even really hunt  but just in case i have the chance )

If given the choice and about the same price, I'll buy 5.56. 

+1. Just because that's my current zero.

Does the Zero change a lot from 5.56 to .223 ?
Never really tried to compare head to head. 

Price and avaibility.

I concur.
 The few times I've been able to buy 223/556 ammo there were deals on 556 making it a little cheaper than 223, no idea why but it doesn't bother me.