556 vs 223

[gregr266]

I realize the pressure difference between the two, but what causes the difference. If I load both with the same powder primer and bullet will the 556 have more pressure built up behind it because the case is a tiny bit thicker and harder so there is less give to it when it goes bang compared to the "weaker" 223 case

[5hundo]

Case thickness has nothing to do with the strength of the load. The only exeption being if you're using a normal load that is not meant to be compressed, and you compress it because the cases are thicker...

The consensus is that 5.56 is safe to shoot in a .223 rifle (say, a bolt-action, for example) but a .223 round might not be safe to shoot in a 5.56 because some hunting loads or other "hot" loads might be too much. Most times, those will be special purpose hunting loads, which would be using commercial brass.

That being said, the condition you have described can effect accuracy because the way the pressure reacts on mis-matched cases can be dissimilar. This is why when people load for accuracy, they match up their cases. When I loaded up my last batch of accuracy .308, I even discriminated R-P cases from one another based on the headstamp. Some hyphens are longer than others, meaning that the brass is from a different lot. I also weighed the cases for consistency...

You can go nuts when doing accuracy loads. I have literally cut a grain of 4064 in half with a razor to get the wieght exactly right. I'm nutty like that...

[a1c]

We need a sticky.

[5hundo]

We need a sticky.

Well, it's not necessarily the usual "Is .223 safe in 5.56mm" question...

It's a legitimate question...

[a1c]

Well, it's not necessarily the usual "Is .223 safe in 5.56mm" question...

It's a legitimate question...

Absolutely. But I suppose we need a 5.56mm vs. .223 sticky that would cover that and more.

[Technical Ted]

The consensus is that 5.56 is safe to shoot in a .223 rifle (say, a bolt-action, for example) but a .223 round might not be safe to shoot in a 5.56 because some hunting loads or other "hot" loads might be too much.

Actually, it's the other way around.

.223 Remington is loaded to SAAMI cartridge specifications. The Sporting Arms and Ammunition Manufacturers' Institute (SAAMI) is a civilian organization that sets the standards for commercial ammuntion.

.223 Remington chamber pressure is 55,000 PSI

In most cases 5.56mm is loaded to NATO specifications for military use.

5.56X45 NATO chamber pressure is 62,000 PSI.

SAAMI warns that 5.56 NATO is unsafe to shoot in a rifle chambered for .223 Remington (scroll down to Centerfire Rifles):

http://www.saami.org/Unsafe_Combinations.cfm

[gregr266]

I understand the chambering issues btwn the rounds, I guess what the real question is what causes the difference in pressure between the two. Is it the actual brass case or is it the load (powder) that one puts in the case.

[Technical Ted]

I understand the chambering issues btwn the rounds, I guess what the real question is what causes the difference in pressure between the two. Is it the actual brass case or is it the load (powder) that one puts in the case.

The type of powder used and the chamber dimensions.

This is a link to a PDF that compares various chamber reamers:

http://www.ar15barrels.com/data/223-556.pdf

[Technical Ted]

Absolutely. But I suppose we need a 5.56mm vs. .223 sticky that would cover that and more.

It's been covered in detail at AR15.com. Why reinvent the wheel?

http://ammo.ar15.com/ammo/

[bohoki]

hmm i too would love to hear if there is a difference loading say a batch of remington .223 cases and a batch of lc 06 brass with the same loadings

which one do you think would have more velocity?


that unsafe combinations thing is hilarious

no 9mm nato in 9mm parabellum guns oh lordy lord

and another thing hits me so are any other cartridges not listed as unsafe are ok?

so its fine to shoot .38 spl in a .45 colt?


i have fired .380 out of a 9mm i guess thats safe cause its not on the list of unsafe combinations

i also see no warnings about firing 32 acp out of a 30 carbine

[Technical Ted]

hmm i too would love to hear if there is a difference loading say a batch of remington .223 cases and a batch of lc 06 brass with the same loadings

which one do you think would have more velocity?

See post #4 for some random data about using mixed brass. Wou;d've been nice if the poster had kept track of which case delivered which velocity (not to mention recipe). Still, the data shows that there is a velocity difference between cases of different manufacturers and therefore different case specifications.

http://www.calguns.net/calgunforum/showthread.php?t=237556

that unsafe combinations thing is hilarious...
i also see no warnings about firing 32 acp out of a 30 carbine

Well, most people are more likely to try to exchange 9mm NATO and 9mm Luger or 9mm Parabellum with one another. Less likely to take a marked box of headstamped 32 ACP and try to load it in a 30 Carbine.