5.56 & .223


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svtruth
February 6, 2011, 11:53 AM
I keep reading that it is OK to chamber .223 in a 5.56 chamber, but not the other way around. So I got to thinking, why did the powers that be make them the same size?
Cartridge development is replete with examples of making more powerful cartridges bigger so they won't chamber in the weaker actions, e.g. .44 mag, .357, etc.

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TexasRifleman
February 6, 2011, 12:00 PM
The leade on the 5.56 is allowed to be longer. Leade is basically the distance the bullet has to travel before it engages the rifling.

For a military style rifle a long leade is good, increases reliability.

On a bolt rifle it's bad, decreases accuracy (theoretically). It also requires a bit less "oomph" in the load since the pressure builds a lot quicker.

So, to make the commercial cartridge more accurate and viable in the market the .223 was introduced. If bolt rifles were chambered for 5.56 they wouldn't, theoretically speaking, be as accurate.

Remington made them basically the same size because that's what the market wanted they thought. Apparently they were right, it's a top selling round.

Also keep in mind that back in '64 when the .223 came out there were not many civilians with access to 5.56 so the idea that shooters might get confused and use the wrong one didn't really occur to anyone I suspect.

That's the way I've always understood it anyway, be interesting to see if others have a different take on it.

The Lone Haranguer
February 6, 2011, 12:35 PM
It has more to do with case wall thickness, chamber pressures and the jump to the rifling (the "leade" that TR refers to) than the dimensions of the cartridge itself.

Coltdriver
February 6, 2011, 02:51 PM
There is a ton on this topic, but the truth is I have never, ever, heard of anyone blowing up their .223 with a 5.56 round.

ball3006
February 6, 2011, 02:56 PM
I shoot both in my TC pistol and I don't notice any difference. chris3

svtruth
February 6, 2011, 04:36 PM
Coltdriver- me neither, hence the question. But I was relieved to find my Kel-Tec PLR is chambered in 5.56 NATO.
Thanks all.

alsaqr
February 6, 2011, 04:52 PM
It has more to do with case wall thickness,


Sorry, case thickness is a myth. For over 40 years i've weighed the cased that are used for my accuracy rounds. US military cases are not thicker than US made commercial .223cases.

Some Brit military cases are much heavier. The heaviest cases i have found are made by Lapua.

http://www.ar15barrels.com/data/223weights.xls

TexasRifleman
February 6, 2011, 04:58 PM
There is a ton on this topic, but the truth is I have never, ever, heard of anyone blowing up their .223 with a 5.56 round.

I have always suspected modern firearms were built strong enough to take it, lawyers and product liability insurance companies being what they are.

Al Thompson
February 6, 2011, 05:19 PM
Not blown up, but running 5.56 in an AR with a .223 chamber can lead to malfunctions. One local guy had an AR come apart on him, a RKI who looked at the rifle told me that the chamber was .223. Probably not the cause, but perhaps a factor.

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