.223 vs 5.56

A

advantagedon

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I recently purchased an AR 15 lower receiver( Stag), it states 5.56 caliber on the side.
I have not yet shot the rifle yet but about a year ago I bought the Bull Barrel upper half.
Put it together, now the upper only has markings M1S on it, I don't know if it is a .223 or a 5.56.....Does it matter???
 
the barrel should say what it's chambered for, usually on the underside. yes it does make a difference because the 5.56 cartridge has a higher chamber pressure than .223. you can shoot .223 out of it either way but make sure the it's chambered for 5.56mm before you shoot that round out of it. there are other subtle differences between 5.56x45mm and .223rem but what it boils down to is you can shoot .223 in a 5.56 but not 5.56 in a .223.
 
I've been hearing that for years, yet no one has ever showed me a documented case where a 223 chambered gun was blown up or damaged because someone shot 5.56 out of it.

I have a Rem 700 BDL Varmint in 223 that since I got it in 1977, I've shot thousands upon thousands of M.193 ball out of. I use to carry M193 in it when I carried in as a CS rifle in LE.

(I was running the AK NG Marksmanship Unit and had access to almost unlimited 5.56).

I also use to use issue it to people shooting 223 chambered ARs in hi power matches.

Another thing about ARs, what they say on the lower and what how the upper is chambered is two different things.

But, (as you will see in further post) there will be lots of scare talk coming forth, which is silly because unless you're shooting military ball/ammo, the stuff you buy is probably 223 which is labeled 5.56 for "tactical" sales purposes.

If in doubt, and you believe all the alarmist, just shoot 223 and don't worry about it.
 
M1S uppers are generally 223 Remington chambered rifles and their quality is not designed to handle actual 5.56 NATO ammunition. Just buy 223 Remington labeled ammunition and shoot. Contact M1S or check to see what chambering your upper has. It could be a 223 Wydle which allows both.
 
I shoot military NATO headstamped SS109 5.56 in my Ruger Mini-14. I use the same, and NATO 5.56 brass loaded to mil spec and max loads, in my Savage 223. I examine every spent casing and have never seen any sign of excess pressure.

The Sierra manual says they are the same thing:
"Remington’s 223, when it was unveiled as the 5.56mm in the AR-15/M16 rifle."
"Surplus military cases add to the popularity of any cartridge, and the 223 has been no exception. If military cases are used, the primer pocket will need to be swaged or reamed to remove the crimp and allow seating of a new primer. Dillon Reloading has a swaging tool specifically for this chore, and it is by far the most satisfactory unit we have used."
 
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The 223 and 556 have more than ~~20,000 psi of safety margin before that primer pocket gets loose.

Compare that with the 22-250, 6mmRem, and 270 that have more like ~~ 2,000 psi of safety margin before the primer pocket gets loose.
 
The Mini-14 IIRC is chambered so both can be used.
There are differences in the chamber dimensions and these differences can be found on the internet . The biggest difference is in the throat.The 5.56 throat is made for the very long heaviest military bullets. This same bullet in the 223 will cause excessive pressure.
 
I have been told and have read (as in I haven't measured for myself) that the difference is in the brass case. Apparently 5.56 brass is slightly thicker allowing for slightly higher pressure. From listed manufacturer's specs it appears that average velocity gains from this pressure increase are <50 fps.

Is there validity to the argument that they are different? Yes.

But -- if you are concerned about such small velocity gains you shouldn't be. Also I am fairly certain that most current .223 chambered rifles have been proof tested far above and beyond true 5.56 pressures. If your rifle fails at 5.56 pressures it going to fail at 223 pressures.

The large majority of the ammo you will find, buy, and shoot will be .223 anyway so no big deal. Other than Lake City stuff true 5.56 ammo isn't very common.
 
I have been told and have read (as in I haven't measured for myself) that the difference is in the brass case. Apparently 5.56 brass is slightly thicker allowing for slightly higher pressure. From listed manufacturer's specs it appears that average velocity gains from this pressure increase are <50 fps
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I was told that putting a tooth under my pillow would bring the tooth fairy-- along with some change. And it always worked.:D

The myth ended when I got older.

Brass cases can vary from one manufacturer to another within the same caliber. It's not that it's 5.56mm brass. It's that it was loaded for the 5.56 NATO CHAMBER.


As such, it's loaded to higher pressure and is suitable for firing in the 5.56 chamber, which has a LONGER THROAT. This does two things.

1. Reduces pressure

2. Insures that, when using heavier bullets seated out longer, they won't stick in the shorter throat of the .223 Rem.

I once chrono'd some PMC NATO 5.56 mm in a Remington M700 .223. Velocity with 55 gr. bullet was 3500 fps. A good 200-300 fps higher than full power .223 ammo I chrono'd thru the same gun.

NOTE: It's also true that military brass tends to be thicker, and can contribute to higher pressure because of less case capacity which produces higher pressure than if fired in a case with more capacity. However, when loaded to the same pressure, the case with the most room in it develops more velocity.
 
Thanks for those links. Winchester website on the LE section used to have an excellent discription but now I can't find it.
 
Brass cases can vary from one manufacturer to another within the same caliber. It's not that it's 5.56mm brass. It's that it was loaded for the 5.56 NATO CHAMBER.


As such, it's loaded to higher pressure and is suitable for firing in the 5.56 chamber, which has a LONGER THROAT. This does two things.

1. Reduces pressure

2. Insures that, when using heavier bullets seated out longer, they won't stick in the shorter throat of the .223 Rem.
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Excellent description. A few more of my brain cells are now working properly.
 
What were they thinking?

Nothing gripes me more than the difference between commercial .223 and .308 and milspec 5.56 and 7.62. What on earth were the ammo makers thinking?

What I have always been told is that 5.56 AR's can use commercial .223, but commercial .223 AR's should not use 5.56. What is stamped on the barrel is what the rifle is chambered for, you can ignore the what is stamped on the magazine well. Anyone correct me if I am wrong. I don't want to pass on bad information.
 
What I have always been told is that 5.56 AR's can use commercial .223, but commercial .223 AR's should not use 5.56. What is stamped on the barrel is what the rifle is chambered for, you can ignore the what is stamped on the magazine well. Anyone correct me if I am wrong. I don't want to pass on bad information.
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This is my understanding as well, but like you, I would also like it explained plainly
 
5.56 AR's can use commercial .223, but commercial .223 AR's should not use 5.56.
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I notice that all these "warnings" invariably include "AR". Not once have I seen bolt guns included in these warnings. Sierra and AA reloading data mention bolt guns in their max loadings: (AA) "<62350Psi
Appliocation: Bolt Action Rifles and Semi Auto Weapons rated for the latest NATO/MIL ammunition." Sierra has a separate "223 Remington (Bolt Action)"

Neither differentiate 5.56. Both specifically include data for heavy and long bullets.
 
Brass cases can vary from one manufacturer to another within the same caliber. It's not that it's 5.56mm brass. It's that it was loaded for the 5.56 NATO CHAMBER.


As such, it's loaded to higher pressure and is suitable for firing in the 5.56 chamber, which has a LONGER THROAT. This does two things.

1. Reduces pressure

2. Insures that, when using heavier bullets seated out longer, they won't stick in the shorter throat of the .223 Rem.
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Riddle me this:

You say the 5.56 has a "longer throat" that wont stick in the shorter chamber of the 223.

OK: Now explain why High Power Shooters who shoot long range (80 + grn bullets) load them longer, to the point they wont fit in the magazine. The Sierra Reloading manual states to load the 80s with an OAL of 2.550. That is much longer then any military round loaded in 5.56 chambers.

I know of no 223 or 5.56 round that can be loaded to magazine length that can come close so long that they present a hazard.
 
One reference on the subject would be Nosler's #6 reloading manual because they list loads and descriptions of both .223 and 5.56.

They don't use the same bullets in their manual stopping the .223 loads at 60 grains and starting the 5.56 loads at 69 grains. Their stated reason is the difference in twist rates for .223 commercial rifles and military platform 5.56, 1 in 12" versus 1 in 8".

What is telling is the max loads listed for 5.56 with 9 grain heavier bullets than .223 with the 6 powders in common. One powder Varget has a .5 grain heavier charge with the heavier bullet in .556. TAC has an identical charge listed and the remaining 4 powders have an average of one grain powder less in .556.

I wouldn't draw too many conclusions from this but I find it of interest.
 
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