I have a .223 rifle and I have been told numerous times not to shoot 5.56x45mm ammo out of it. I reload and I checked out the differences in the casing between the two and I can see no difference in dimensions. I assume the difference is in the loading and not the casing. Is this a true statement? I have an opportunity to buy brand new 5.56x45mm unprimed brass at a good price and I want to know if I can use it for my .223 reloads with no problems. I know this seems like a dumb question but I just want to be sure I am not missing something that is right there in front of my face. 

Thanks again for any help and suggestions!!!

As I understand it, the external dimensions of the two cases are identical, but the wall thickness and whatnot is not.  The 5.56 case is heavier walled, which reduces internal volume and increases pressure, making them unsafe to shoot out of a .223 chamber. 

Here's an excerpt from a thread on the topic at AR15.com

This from federal le site:

The Difference Between 223 Rem and 5.56 Military Cartridges
There is a general misperception by the shooting public that the 223 Rem and 5.56 Military cartridges are identical – just different designations for commercial and military – and can routinely be interchanged. The fact however is that, although somewhat similar, they are not the same.
•
The cartridge casings of each have basically the same length and exterior dimensions.
•
Mil Spec 5.56 ammo typically has higher velocity and chamber pressure than the 223 Rem.
•
The 5.56 cartridge case may have a thicker sidewall and a thicker head - to better withstand the stresses generated by the higher chamber pressures. This, however, reduces the powder capacity of the case - which is of concern to the reloader.
•
The 5.56mm and 223 Rem. chambers are similar but not identical. The difference is in the “Leade”. Leade is defined as a portion of the barrel directly in front of the chamber where the rifling has been conically removed to allow room for the seated bullet. This portion of the chamber is more commonly known as the throat. Leade in a 223 Rem. chamber is usually .085”. In a 5.56mm chamber the leade is typically .162”, or almost twice as much as in the 223 Rem. chamber.
•
You can fire 223 Rem. cartridges in 5.56mm chambers with this longer leade, but you will generally have a slight loss in accuracy and velocity – compared to firing the 223 round in the chamber with the shorter leade it was designed for.
•
Problems may occur when firing the higher pressure 5.56mm cartridge in a 223 chamber with its much shorter leade. It is generally known that shortening the leade can dramatically increase chamber pressure. In some cases, this higher pressure could result in primer pocket gas leaks, blown cartridge case heads, and gun functioning issues.
•
The 5.56mm military cartridge fired in a 223 Rem. chamber is considered by SAAMI (Small Arms and Ammunition Manufacturers Institute) to be an unsafe ammunition combination and is listed in the “Unsafe Arms and Ammunition Combinations” Section of the SAAMI Technical Correspondent’s Handbook. It clearly states; “In firearms chambered for 223 Rem – do not use 5.56 Military cartridges.” Federal Cartridge is a member of SAAMI and supports this position.
•
Federal’s XM193 packaging currently has a warning that states “For use in standard 5.56 Chambers. Do not use in non-standard 5.56 chambers.” This warning is also listed on the XM193 Product Specification Sheet. Winchester also has a similar warning on their USA brand 5.56 ammunition packaging: “Use only in firearms in good condition designed and chambered by firearm manufacturer specifically for this 5.56 ammunition and so marked on the firearm.”
•
It is our understanding that commercially available AR15’s and M16’s – although some are stamped 223 Rem on the receiver – are manufactured with 5.56 chambers. Our advice however should be that it is the customer’s responsibility to know what their firearm is chambered for and choose their ammo accordingly.

As I understand it, the external dimensions of the two cases are identical, but the wall thickness and whatnot is not.  The 5.56 case is heavier walled, which reduces internal volume and increases pressure, making them unsafe to shoot out of a .223 chamber. 

Here's an excerpt from a thread on the topic at AR15.com

Quote

This from federal le site:

The Difference Between 223 Rem and 5.56 Military Cartridges
There is a general misperception by the shooting public that the 223 Rem and 5.56 Military cartridges are identical – just different designations for commercial and military – and can routinely be interchanged. The fact however is that, although somewhat similar, they are not the same.
•
The cartridge casings of each have basically the same length and exterior dimensions.
•
Mil Spec 5.56 ammo typically has higher velocity and chamber pressure than the 223 Rem.
•
The 5.56 cartridge case may have a thicker sidewall and a thicker head - to better withstand the stresses generated by the higher chamber pressures. This, however, reduces the powder capacity of the case - which is of concern to the reloader.
•
The 5.56mm and 223 Rem. chambers are similar but not identical. The difference is in the “Leade”. Leade is defined as a portion of the barrel directly in front of the chamber where the rifling has been conically removed to allow room for the seated bullet. This portion of the chamber is more commonly known as the throat. Leade in a 223 Rem. chamber is usually .085”. In a 5.56mm chamber the leade is typically .162”, or almost twice as much as in the 223 Rem. chamber.
•
You can fire 223 Rem. cartridges in 5.56mm chambers with this longer leade, but you will generally have a slight loss in accuracy and velocity – compared to firing the 223 round in the chamber with the shorter leade it was designed for.
•
Problems may occur when firing the higher pressure 5.56mm cartridge in a 223 chamber with its much shorter leade. It is generally known that shortening the leade can dramatically increase chamber pressure. In some cases, this higher pressure could result in primer pocket gas leaks, blown cartridge case heads, and gun functioning issues.
•
The 5.56mm military cartridge fired in a 223 Rem. chamber is considered by SAAMI (Small Arms and Ammunition Manufacturers Institute) to be an unsafe ammunition combination and is listed in the “Unsafe Arms and Ammunition Combinations” Section of the SAAMI Technical Correspondent’s Handbook. It clearly states; “In firearms chambered for 223 Rem – do not use 5.56 Military cartridges.” Federal Cartridge is a member of SAAMI and supports this position.
•
Federal’s XM193 packaging currently has a warning that states “For use in standard 5.56 Chambers. Do not use in non-standard 5.56 chambers.” This warning is also listed on the XM193 Product Specification Sheet. Winchester also has a similar warning on their USA brand 5.56 ammunition packaging: “Use only in firearms in good condition designed and chambered by firearm manufacturer specifically for this 5.56 ammunition and so marked on the firearm.”
•
It is our understanding that commercially available AR15’s and M16’s – although some are stamped 223 Rem on the receiver – are manufactured with 5.56 chambers. Our advice however should be that it is the customer’s responsibility to know what their firearm is chambered for and choose their ammo accordingly.

Thanks for this. Up until now I had not been able to find anything that adequately explains the differences.

Thanks again!!!

There are slight dimensional differences between .223 Rem and 5.56 NATO, both exterior and wall thickness. 

The big difference between the two is the 5.56 NATO is allowed per SAAMI to load to higher pressures.

For the unprimed brass, yes go ahead and buy it.  If you are loading for .223 Rem, just be sure to follow the load data for that instead of the NATO cartridge.  Realistically though, for most current/modern firearms there isn't much of a safety concern.

There are slight dimensional differences between .223 Rem and 5.56 NATO, both exterior and wall thickness. 

For the unprimed brass, yes go ahead and buy it.  If you are loading for .223 Rem, just be sure to follow the load data for that instead of the NATO cartridge.  Realistically though, for most current/modern firearms there isn't much of a safety concern.

5.56 NATO brass can be thicker.  This is not always true, it is manufacturer dependent.  LC (Lake City) being the most common.

So you are telling him to use the same charge that you would load in .223? 

Thicker case wall = less room+same charge as .223 = higher chamber pressure. 


Do you reload 5.56 GZIRE?

After doing some more research I decided to go ahead and buy the brass. In case anyone is interested it is LC (Lake Ciy) brass at $109.99 for 1,000 at Midway. Plus $23.34 for shipping. Today is the last day for the sale. They had 500 for $59.99 earlier today but I don't see it available any more. Hard to beat at $.013 per case!!! 

Quote from: GZire on December 12, 2011, 09:39:39 AM

There are slight dimensional differences between .223 Rem and 5.56 NATO, both exterior and wall thickness. 

For the unprimed brass, yes go ahead and buy it.  If you are loading for .223 Rem, just be sure to follow the load data for that instead of the NATO cartridge.  Realistically though, for most current/modern firearms there isn't much of a safety concern.

5.56 NATO brass can be thicker.  This is not always true, it is manufacturer dependent.  LC (Lake City) being the most common.

So you are telling him to use the same charge that you would load in .223? 

Thicker case wall = less room+same charge as .223 = higher chamber pressure. 


Do you reload 5.56 GZIRE?

Yup I reload.  Typically I go middle of the road when reloading, I don't push the upper or lower ends for the load data.

........and yes I'd use the .223 Rem load data, middle of the data table, or hug the lower end if he's concerned.  Personally I am not too concerned when dealing with current/modern firearms.

I'm not trying to start a dick-measuring contest or anything, but some of the safety factors that you're relying on with modern firearms and ammunition is due to everything being in accordance with SAAMI specs.  If you're operating outside of SAAMI specs, or in the case of 5.56/.223 deliberately ignoring them, you're eating into that safety margin.  Will your gun blow up in your face and shoot pieces back into your brain, a la Sin City?  Probably not, all other things being equal.  However, if you get a case that's got substantially thicker case walls than the rest of the lot for some reason, and then that case gets a little extra powder, you may have a massive issue because you're already outside the safe operating zone. 

If you decide to press on, more power to you, but when I touch off a chain reaction that causes something to be pressurized to around 50,000 psi, 4 inches from my face, I want to be damn sure the experts say, "Yup, this is safe."  In this case, they universally say, "Do not do this." 

Quote from: vooduchikn on December 12, 2011, 11:24:47 AM

Quote from: GZire on December 12, 2011, 09:39:39 AM

There are slight dimensional differences between .223 Rem and 5.56 NATO, both exterior and wall thickness. 

For the unprimed brass, yes go ahead and buy it.  If you are loading for .223 Rem, just be sure to follow the load data for that instead of the NATO cartridge.  Realistically though, for most current/modern firearms there isn't much of a safety concern.

5.56 NATO brass can be thicker.  This is not always true, it is manufacturer dependent.  LC (Lake City) being the most common.

So you are telling him to use the same charge that you would load in .223? 

Thicker case wall = less room+same charge as .223 = higher chamber pressure. 


Do you reload 5.56 GZIRE?

Yup I reload.  Typically I go middle of the road when reloading, I don't push the upper or lower ends for the load data.

........and yes I'd use the .223 Rem load data, middle of the data table, or hug the lower end if he's concerned.  Personally I am not too concerned when dealing with current/modern firearms.

Just so everyone knows I will work my loads up from the bottom as I always do. Not to worry about high pressure loads as I will watch out for the telltale signs. Also, I'll weigh the cases and look for any heavy weights and compare them to what I am using  now (Federal once fired). My rifle is a bolt action Rem 700 with a 24" bull barrel. I was worried about not being able to resize the cases properly in my .223 dies. Now that I know I can I have some new cases on the way.

All of this research I have done combined with the answers I received here does confirm something I noticed while picking up various brass from someone shooting next to me. When their gun is a .223 and they shoot .223 out of it the brass looks like it should. Same went for the 5.56. But twice now when I ran across someone with a 5.56 shooting .223 out of it the shoulders of the case were discolored. And I couldn't figure out why. Now I think I understand why.

Quote from: vooduchikn on December 12, 2011, 11:24:47 AM

Quote from: GZire on December 12, 2011, 09:39:39 AM

There are slight dimensional differences between .223 Rem and 5.56 NATO, both exterior and wall thickness. 

For the unprimed brass, yes go ahead and buy it.  If you are loading for .223 Rem, just be sure to follow the load data for that instead of the NATO cartridge.  Realistically though, for most current/modern firearms there isn't much of a safety concern.

5.56 NATO brass can be thicker.  This is not always true, it is manufacturer dependent.  LC (Lake City) being the most common.

So you are telling him to use the same charge that you would load in .223? 

Thicker case wall = less room+same charge as .223 = higher chamber pressure. 


Do you reload 5.56 GZIRE?

Yup I reload.  Typically I go middle of the road when reloading, I don't push the upper or lower ends for the load data.

........and yes I'd use the .223 Rem load data, middle of the data table, or hug the lower end if he's concerned.  Personally I am not too concerned when dealing with current/modern firearms.

So do I. I was wondering if you might want to swap recipes.

I am using LC Military brass...let me know.

I'm not trying to start a dick-measuring contest or anything, but some of the safety factors that you're relying on with modern firearms and ammunition is due to everything being in accordance with SAAMI specs.  If you're operating outside of SAAMI specs, or in the case of 5.56/.223 deliberately ignoring them, you're eating into that safety margin.  Will your gun blow up in your face and shoot pieces back into your brain, a la Sin City?  Probably not, all other things being equal.  However, if you get a case that's got substantially thicker case walls than the rest of the lot for some reason, and then that case gets a little extra powder, you may have a massive issue because you're already outside the safe operating zone. 

If you decide to press on, more power to you, but when I touch off a chain reaction that causes something to be pressurized to around 50,000 psi, 4 inches from my face, I want to be damn sure the experts say, "Yup, this is safe."  In this case, they universally say, "Do not do this."

Well if we're going to get into that degree, then...............you should be using the same case and primer as the book as well.  How often do we do that?  I've got Sierra, Speer, Nosler, & Barnes manuals to name a few and no way in hell those 4 cover all the possible combinations out there.  The data is given to you with one case and one primer, you cannot tell me that you are loading with the exact same materials that the books indicate in all of your reloads.  For me at most I'm covering 4 cases and there's no guarantee that I'm using the correct primer for that case, but again by the (SAAMI) book we shouldn't be doing it.

I am not condoning substituting of powders or anything along those lines.

To be clear I am saying (for the 3rd time) to load to .223 Rem standards not 5.56 NATO.  If you feel that the cases are so thick that they will cut the interior volume of a .223 case so much that you run into over-pressurization, then IMHO there's a lot of other issues going on with the manufacturer's QC process and you will see a lot of incidents popping up.

Just so everyone knows I will work my loads up from the bottom as I always do. Not to worry about high pressure loads as I will watch out for the telltale signs. Also, I'll weigh the cases and look for any heavy weights and compare them to what I am using  now (Federal once fired). My rifle is a bolt action Rem 700 with a 24" bull barrel. I was worried about not being able to resize the cases properly in my .223 dies. Now that I know I can I have some new cases on the way.

All of this research I have done combined with the answers I received here does confirm something I noticed while picking up various brass from someone shooting next to me. When their gun is a .223 and they shoot .223 out of it the brass looks like it should. Same went for the 5.56. But twice now when I ran across someone with a 5.56 shooting .223 out of it the shoulders of the case were discolored. And I couldn't figure out why. Now I think I understand why.

The case shoulders are probably discolored to to case annealing (during the case fabrication process).  If you're talking about deformation due to flow of the brass to fill the chamber of the rifle, IMHO you cannot readily see that with the naked eye.  If you're talking about case splitting/thinning, then that is something you can see with the naked eye.  If you are talking discolored as in from carbon, then yes there might be some concern there, but not if you're shooting a HK9X series rifle due to their chamber fluting.

To clarify again you are concerned with 5.56 NATO in a .223 Rem because NATO will allow higher pressures per SAAMI (and keep in mind they aren't the only guys out there that set standards).  With the .308 Win vs. 7.62 NATO you are worried about the opposite.  .308 Win allows higher pressures per SAAMI than does the NATO cartridge. 

............and finally to confuse you even more, you can also be seeing a person shooting a Wylde chamber too..........