How much alike are .223 Rem & 5.56 NATO?

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AZ_M&P

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I'm picking up a new M&P 15 OR next week chambered in .223 Remington, and I understand the rifle can also fire the 5.56 NATO rounds. I have some spent brass from both calibers and for all intents they appear the same, and I can't find any loads for just the 5.56. In fact, my Lyman manual lists the .223 as ".223/5.56".

My question - Can I run my 5.56 brass through a .223 die set? Or aren't they that interchangeable?:confused:
 
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There is no difference between 223 and 556 brass. There are, however, differences between various manufacturer's versions (and batches) of each brass type. Some will be heavier (thicker walls = less powder capacity, smaller effective chamber, slightly higher pressures). 556 ammo is often military, and so will have a crimp to seal the primer in place. This crimp must be removed after decapping, either by swaging or reaming.

The difference is in the firearm's chamber design with the 556 allowing higher pressures safely. So while a 556 round can be chambered and fired from a 223, the chamber is not designed for the pressures that can result. Of course 223 can be fired from a 556 chamber without issues.

There are other chambers (eg Wylde) that can also handle both types of loads.

Bottom line: If you have a 223 rifle, use either brass type, watch for crimped primer pockets and deal with them, and 223 load data.
 
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As was stated - after firing the brass is the same. This is also supported by the fact that one can't buy 5.56 dies.

If it is "chambered in .223 but can fire 5.56" - that would mean it's 5.56. But check the barrel.

In addition to 5.56 chambers being able to handle higher pressure, I believe the 5.56 spec also calls for longer leade(?) than .223 - so the bullet profile can extend a bit further than the .223. This, in addition to the higher pressure, is why you don't want to put 5.56 rounds in .223 chamber.

Also, for pure plinking rounds, I completely interchange .223 and 5.56 brass. I make no effort to seperate them or handle them differently. Both cases are processed (i.e. the processes I use) exactly the same. I don't load things differently based on the brass differences Twoboxer described. I figure that level of difference, for plinking rounds, represent differences in levels of accuracy that my skill set is not able to discern.

OR
 
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AZ_M&P said:
I'm picking up a new M&P 15 OR next week chambered in .223 Remington, and I understand the rifle can also fire the 5.56 NATO rounds. I have some spent brass from both calibers and for all intents they appear the same, and I can't find any loads for just the 5.56. In fact, my Lyman manual lists the .223 as ".223/5.56".

My question - Can I run my 5.56 brass through a .223 die set? Or aren't they that interchangeable?:confused:
Click to expand...


As smokingdog stated. Your rifle is chamber in 5.56 not 223 Rem

You can shoot 223 or 5.56 ammo in it. Once you reload 5.56 there is no difference.

Load data for 5.56 is listed under "service rifle" loads all it means is they are a bit "hotter" Really no need to even bother with them.

There are no 5.56 reloading dies. They are listed as 223 Rem.

With 5.56 marked brass it is usually crimped primers so after you resize them you need to remove the crimp or you will not be able to reprime them. You can ream them out or use a swagging tool.
 
To answer the OP's question directly.....yes, you can certainly run 5.56 NATO through your .223 Rem. dies.

The outer dimensions of the two cartridges are IDENTICAL. Some 5.56 NATO brass is slightly thicker-walled than commercial .223 brass. This will only cause a bit more difficulty in resizing the cases, as the expander ball will be a bit tighter in the necks. It may lead to trimming the cases a bit more often. But, there are differences in commercial .223 case wall thicknesses, as well. Thicker-walled .223 brass will produce more pressure than thinner-walled brass. However, that is not a problem, unless loaded to the maximum end of the load range.

The real issue with interchanging the two cartridges is not the cases - but the chambers of the firearms in which they will be fired. Military (5.56 NATO) chambers tend to be longer than commercial .223 chambers. So, it can be a problem to shoot 5.56 NATO ammo, if loaded HOT, in the shorter commercial chambers.

Loading SAFE .223 Rem. loads in 5.56 cases, however, is NOT a problem. In fact, I use mostly 5.56 brass, resized with a .223 die, in my Savage .223 rifle. My loads are NOT hot ones.
Function, pressures and accuracy in my rifle are indistinguishable from using .223 brass.
 
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Thank you all, this is my first AR and you've provided a lot of good information.

Merry Christmas!
 
Like already said, the difference in the rifles themselves is the chamber. Just for instance I have one bolt action rifle in .223 Remington and also AR-15 rifles. Using Hornady's popular 55 grain FMJ bullet, if I seat the bullet to an overall cartridge length at 2.246" the bullet will just touch the rifling of the barrel in the .223 Remington chamber. In 2 different makes of AR-15's one rifle for the same bullet to just touch the rifling the length would be 2.370" in one and 2.390" in the other. The longer jump to the rifling in AR15 in 5.56 chambers keeps pressure down. So a bullet seated to the maximum magazine length at 2.260" the overall length would not allow the bolt to close in the .223 bolt rifle. Different rifles and the chamber length may differ from mine. In the 5.56 AR's a 55 grain bullet is almost falling out of the case neck at 2.370-2.390".
 
5.56 / 223 Delta

I am pretty sure that your rifle will be chambered I 5.56 Nato. In that case you can shoot either. You tube has several videos on this matter. If you ever reload you can find 5.56 load data on the Accurate and Ram Shot sites !
 
I am not new to reloading .223 but I have never owned a rifle marked or designed for 5.56 military cartridges. I’d like my impression of the difference in their chambers verified and perhaps give the O.P. a better understanding of the differences while we’re discussing them. It has always been common for U.S. military rifles to have sloppier chamber body diameter and head space than the manufacturers of quality commercial sporting rifles allow. Over looking that the chambers are the same up to the end of the case neck. The difference is in the ball seat, the cylindrical area ahead of the case neck before the start of rifling, and the lead or throat ahead of it. 5.56s are cut some what like Roy Weatherby’s fee bored magnum chambers. The longer free bore or throat reduces pressure. Weatherby’s cartridges are not intended to stay within their designed pressure limits if they are fired in rifles that were not free bored. As I understand it the same could be said of military 5.56 mm cartridges. They are not intended to produce higher pressures than commercial .223 cartridges but will do so if they are fired in barrels that are not throated longer for them. However, the pressure increase firing G.I. 5.56 mm cartridges in commercial .223 barrels is far less than the safety margin in their strength.

Am I wrong?

Edit to add: I did not see rg1's reply before posting. His rifles demonstrate the difference in throats.
 
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1. The European CIP the equivalent of the American SAAMI considers the .223 and 5.56 to be one in the same cartridge.

2. Do not let European metric system confuse the issue, the 30-06 is called the 7.62×63mm and the .308 is the 7.62x51 in Europe. (silly metric system) :D

3. Both the .223 and the 5.56 are loaded to the exact same chamber pressure of 52,000 cup or 55,000 psi. (American SAAMI)

4. Lake City 5.56 cases are "NOT" thicker, they are in fact made harder than commercial .223 case to better withstand larger diameter military chamber.

556hard-a_zps7570e6b0.jpg


hardness-a_zps8d54ad66.jpg


Below is an excerpt from CatShooters posting on .223/5.56 brass hardness At AccurateShooter.com.

The actual Hardness measurements were (.062"x100kg, Rockwell "B")

LC 2008 = 96

Lapua 223 Match = 86

Norma = 76

Winchester 223 = 69

Remington "R-P" = 49

For all you guys that have been saying that Winchester cases were tougher than Remington... you are vindicated, they are a lot tougher!... 40% tougher

For all you guys that think Lake City is surplus junk, nothing could be further from the truth. It is some of the most bestest brass made (it is paid for by the tax payer), so enjoy it!!!

LC and Lapua are the "The pick of the litter"!


5. The only difference between the .223 and 5.56 is the throat. But this also varies between manufactures, the throat in my Savage .223 with a 1 in 9 twist is longer than my AR15 rifles.

223_zps6248614d.jpg


Look at line "N" at the various throat lengths, My Savage has a throat length of 0.0566 and longer than the military of 0.0500

223-556_zpsf4f56449.jpg


Below the milspec requirements for commercial contract 5.56 ammunition made for the military. Please note line 3.7 and chamber pressure of 55,000 psi.

m855specs_zps15389a22.jpg


And below from a Army TM manual again stating a chamber pressure of 55,000 psi.

PagesfromTM43-0001-27_CHG-2-2_zps377343cc.jpg


Below shows the Lake City cases have the "MOST" case capacity. (and not thicker like the LC 7.62)

casecap_zps3f8bb2c9.jpg


Bottom line all military chambers are larger in diameter and longer in headspace settings than there civilian counter parts to ensure functioning under combat combat conditions. And Lake City brass is made Ford Truck Tough "and" high quality brass.

And if you shoot military 5.56 M855 ammunition in a short throated .223 the chamber pressure will be approximately 5,000 psi higher. These rifles will be the ones with a 1 in 14 or 1 in 12 twist and the shorter throat.
 
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The OP may find this a little less technical and easier to swallow.:)

Clicking on the boxes of Sierra Bullets will bring up data for 223 BOLT and 5.56 AR loads.

Using a AR or any semi auto you need to full size the brass every time. Bolt action you can neck size several times before needing a full case resize.

You also will get a better idea of bullet weights for the specific twist of your rifle.(1:9)

223 Rem + 223 AI Cartridge Guide
 
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