5.56mm NATO versus 223 Remington Chamber Differences

[DTHN2LGS]

No, you should also have a Field gauge too in order to check if the chamber is too deep or not. If the bolt closes on a Field gauge, do NOT fire the gun!

[Turnkey11]

I was always just told the pressures of a 5.56 round would somehow damage a rifle chambered in 223. This definitely was helpful. Much appreciated.

Ive never witnessed damage to the gun, but Ive seen the brass get stuck in the chamber, consistently.

[Tweak]

So, all I need to check my chamber is a 5.56 GO gauge and if the action closes on the guage I have a 5.56 chamber? Am I reading this correctly?

No, you are not.

A headspace gage measures the headspace dimension (bolt face to datum line on shoulder) whereas the difference between 5.56 and .223 is primarily in the throat.

[patrick sweeney]

Simple: the military is willing to have more headspace, as they don't care if a case is reloadable or not. As long as headspace is not so great that cases separate, and tie up the weapon, they're cool with it.

Yes. According to the data I've seen No go for .223 Rem is 1.4666" and No go for 5.56 is 1.4736". Why the difference if the cases of .223 and 5.56 are the same dimension from the cartridge base to shoulder.

For instance, if I mounted a new barrel labeled .223 Rem and the bolt would close on a No go 1.4666" gauge the bolt/barrel headspace would be out of spec. but would not be out of spec if it were a 5.56 Nato chamber.

As for a gauge, to tell if a chamber is .223 or 5.56 (and the barrel, with some exceptions, will not tell you the truth) you need one of Ned Christiansen's 223/556 gauges.

http://www.m-guns.com/tools.php

[bombim]

I have a 5.56mm chamber and have shot only 5.56mm ammo. Lately,
I've been offered .223 Rem ammo cheaper than my regular 5.56mm so
I'm thinking of trying them on my AR.

Can I safely have .223 shells reloaded to 5.56? If not, I would
I have to keep track of the shells and ensure that they are
correctly segregated. It would add an element of danger if I
were to make a mistake.

[Tweak]

You can shoot .223 in a 5.56 chamber, the concern, mostly un-warranted, is 5.56 in a .223 chamber.

[patrick sweeney]

You can easily and safely reload .223, and use it in your 5.56. (If indeed you do have a 5.56 leade/throat) .223 in a 5.56 is not a problem, it is the reverse that can be a problem.

The brass is (within normal manufacturing variances) the same, the difference being the pressure. Use .223 load data, and have fun.

To load to 5.56, you would simply exceed the .223 load data by the amount specified by reloading manuals, to create 5.56. Don't bother.

If you really need 5.56, buy 5.56. If you're reloading, the point is to lower costs and wear-and-tear, so stick with the .223 data.

And yes, Tweak, it can matter.

[Iraqgunz]

I disagree. I have seen numerous carbines from XYZ manufacturers that had failure to extract issues when using 5.56 in their .223 chmabered AR's.

Specifically, Bushamster, DPMS and Oly Arms.

You can shoot .223 in a 5.56 chamber, the concern, mostly un-warranted, is 5.56 in a .223 chamber.

[Tweak]

And yes, Tweak, it can matter.

Never said it couldn't.

Specifically, Bushamster, DPMS and Oly Arms.

Yep, and usually those POS have tight headspace and often undersized chambers. The SAAMI warnings came out in response to folks using milsurp in their civilian bolt guns. 5.56 in a tight .223 will show pressure signs. SAAMI is more concerned about 50,000 psi to the face than the occasional malfunction.

There's an excellent thread over on Brand X where I was helping a PD armorer with his stock of duty rifles. He went all out in testing the chambers to include chronographing, casting the chambers and checking the headspace.

The information was so telling that one maker applied pressure to his chain of command to shut him up.

I've done tests of problem (OAI) .223 chambers using only a 5.56 throat (no change to headspace) reamer then a no throat .223 reamer. In every case opening the throat to 5.56 didn't change the malfunctions but cutting the chamber (usually saw chips on the body on a no pressure pass) to a proper .223 or deepening the headspace (chips on shoulder with pressure) did solve the problem.

If a rifle needs to have the bolt pried open on a .223 NOGO then it's probably not going to run 5.56 when it gets hot.

If the minor differences in throat profiles made such a catastrophic difference then rifles would be popping all day around the world.

Throat profile is way down the list of potential causes of malfunctions.

[patrick sweeney]

[shrug]

My experience differs. When we see problematic rifles in the classes, I don't even bother bringing out the headspace gages any more. I simply measure the threat/leade, and if the gage is at all sticky, ream just that.

9+ times out of 10, that solves the problem. The ones it doesn't have a lot more problems than just the throat/leade.