Odd question 5.556 vs .223

[dustoffer]

When I first heard this "can't shoot" stuff I called BS on it and contacted the experts at Sierra Bullets--and they slathered the BS all over it too. Only difference is typically the rifling twist rate which has an affect on what weight/length bullets perform best.

Internet rumor at best.

[TxNurse]

When I first heard this "can't shoot" stuff I called BS on it and contacted the experts at Sierra Bullets--and they slathered the BS all over it too. Only difference is typically the rifling twist rate which has an affect on what weight/length bullets perform best.

Internet rumor at best.

Chamber dimensions and pressure have little to nothing to do with rifling twist rate. There are differences in dimensions between 5.56 and .223 chambers.

[Jäger]

if your really worried about it here's what you do

1. stop reading 5.56 vs .223 stuff on the internet
2. select a bullet that you think would work well doing whatever you want the rifle to do. ie hunting, plinking, self defense (don't worry about bullet weight)
3. shoot said bullet to see how your gun likes it. if you cant get your desired accuracy return to step 2.
4. if this rifle will fill a defensive role shoot your selected bullet ALOT to make sure its reliable, ie zero malfunctions period.

[meltingfeather]

Bottom line is that different pressures (loads) yield different trajectories, yes. Enough to worry about? It depends on how much trajectory you're using (100 yds. vs. 400 yds.), but probably not. If you're feeding your rifle with a 4x scope on it different ammo, you're probably not concerned about pinpoint accuracy at 400 yards, so you're probably all good.
It's not as easy as "one has higher pressure." 5.56 is not standardized by SAAMI and the pressure testing methods used by SAAMI and the military are different, so it's a bit of apples to oranges.
It's also not as easy as "you can't shoot 5.56 out of a .223 barrel." It's possible that in doing so you might exceed the SAAMI rating for your chamber, but little is known about what actually happens if you do that. If your barrel was proof tested then it has had at least one round well above the design pressure through it.
The easy thing to do is shoot the ammo that's stamped on your barrel, which I think most people get.

[LWD]

The Hornady 75 gr BTHP will stabilize in a 1:9" twist barrel. Nosler's and Sierra's 77 grain bullets probably won't but might. The Hornady 75 gr AMax will not.

.223 Remington has a SAAMI specification. 5.56mm ammo does not. The pressure of 5.56mm ammo will depend on who loaded it. If you encounter 5.56mm ammo with what is called a circle cross head stamp (think plus sign in a circle), don't shoot it in a .223 chamber. The circle cross headstamp is a NATO indicator. 5.56mm ammo with it is almost certainly loaded to 60,000+ psi. 5.56mm ammo from a domestic manufacturer may or may not be.

Most people think about twist rate waaaay too much. Unless you're shooting bench rest the only question you need to answer is is my barrel fast enough to stabilize the bullet I want to shoot. If it's faster, no worries. The only exception to this is shooting light weight, highly frangible varmint bullets in a really fast twist barrel. A Sierra 40 gr Blitz or Hornady SPSX will likely be vaporized by a 1:7" twist barrel—the centrifugal forces will tear them apart.

LWD

[Drycreek3189]

With post # 18, 19, and 20, You should now know more than enough about your question OP. Best explanations I've seen so far !

[Pushbutton2]

Thank you

[Pthomas]

Same round 556 is the nato designator for 223