Is there a difference, if so what is it....OldYooper.

The difference seems to be mostly in the chamber of the rifle.

Some 5.56 X 45mm brass has a thicker web on the case head and some also have thicker case walls. But, based on reloaders that I trust, there are some .223 Remington brass that have thicker webbing at the heads and walls. They weighed various brass from each cartridge and the bag was mixed. Some .223 Remington cases were heavier and some 5.56 X 45mm cases were heavier.

The powder charge may be a bit hotter with 5.56 X 45mm but I don't recall anyone confirming that and reloading information for 5.56 X 45mm is not common to find. It's out there but you really have to look for it.

Since the experienced reloaders I know all reload .223 Remington instead of 5.56X45mm, I'm guessing the difference in the cartridges isn't enough for them to bother with.

Hi Yoop,

5.56 and .223 brass outside dimensions are the same. 5.56 brass is typically heavier/thicker wall. So, either will chamber in your AR.

Loaded 5.56 NATO ammo does have higher pressures than .223, (internal volume) so you should check your receiver markings or consult your manufacturer for specifics as to what it’s designed for.

There are many articles explaining this online too that are very helpful.

Regards, Mark

all ammo brass brands varies in internal volume and weight. my routine is to practice using one manufacturer and use that brass for reloading. when I wear it out and need new brass, if i change brands, I recheck my load as internal capacity can change. Right now I have a .308 bucket of LC and one of CAVIM. same in 30.06( HXP and LC) and .223(MAL and LC) all reload fine, but there is a weight difference and hence probably an internal volume difference

If you work up a load using commercial 223 brass in your particular rifle no problem. However if you then come into a batch of military brass (primarily LC / Lake City brass) conventional wisdom is that you need to back your powder charges off 10% and work back up, due to reduced internal volume of mil-spec brass which will increase pressures.

I mix "em" load "em" and shoot "em"........25 years. Never a problem.

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S&W Accumulator

I load them all the same and have never had any issues. If you are loading so close to max that the difference in the brass makes a difference then use one kind of brass.

You said brass. Is that what you meant or did you mean (loaded) ammo? There's a difference.

The brass itself doesn't really make it one or the other since so many companies just change headstamps on the same case & their external dimensions are the same.

It's the pressure it's loaded to, as well as the chamber's dimensions it's fired in matters.

.223 Remington & 5.56 NATO have slightly different chambers.

5.56 NATO chambers have a longer leade/throat to handle bullets of different design & longer ogives.

Firing a 5.56 NATO round in the shorter leade/throat of a .223 chamber can cause abnormally high pressures because the bullet was forced into the rifling when chambered.

If your AR-15 is marked for both cartridges then rounds loaded to either spec can be safely fired in it.

.

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Waiting for the break of day

What he said +1!

The issue has been covered here as well as in other threads and other forums.
The main problem is shooter induced. Treat all the cases as if they are .223 Rem and use .223 Rem load data/recipe exactly and you will be GTG!

Use Surplus 5.56 NATO rated ammo in firearms designated for 5.56 NATO! Use .223 Rem in either.

Smiles,

This is a good explanation (I thought) of the variations and what to be aware of:

That's my understanding. Leades are longer for 5.56 to accommodate longer (heavier) bullets. I use 5.56 brass (LC) exclusively but use .223 load data. I use my reloads in both 5.56 x 45 and .223 rifles. I use 62 grn bullets for all my loads.

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That's just somebody talkin.

If you're a handloader, consider reading that section in most handloading manuals. It's well-explained. Save YouTube as a last resort until you have a basic knowledge. You may find you don't need YouTube at all.

There have been several threads on this subject. The 5.56 x 45 MM cartridge was developed as a military round by Remington. This included the case specifications. Rebranding to .223 (but with a lower peak pressure) to help capture civilian sales was an afterthought.

Decades back there was a story that went around that the pressure difference was due to the differences between SAAMI and DOD chronograph distances (15 feet to center of screens vs 78 feet between center of screens. Why? Because that was how it had to be done way back when and no one wants to rewrite all the manuals, specifications etc.) It was easier to slightly jack up the pressure of the military round than to restart design over a few f/s short of desired velocity.

Anyhow, in most .223/5.56 mm brass there really isn't a significant difference in capacity regardless within the same brand of brass. But, it does pay to be cautious.

I need to add that i was sticking with one head stamp because I was loading for match ammo. I built up my load for 600 yd using one headstamp, one primer, one bullet. the other courses of fire, my offhand sometimes could have been shot using 12ga 00 buck....

Were I a benchrest competitor, I would use only one brand of brass, segregated by weight.


Since I'm not, my 223/556 brass goes into a bucket and it reloaded indiscriminately.