5.56mm & .223 Remington

JRDANIELS · August 7, 2009, 07:27 PM

Whats the real story? Exact same? 5.56 has a little thicker case? Never understood the actual differance. Whats the real story here? And, is it ok to fire 5.56mm ammo in a .223 chamber and also ok to fire .223 in a 5.56mm chamber?

Art Eatman · August 7, 2009, 07:48 PM

As near as I can tell from the numberous articles and discussions, the primary difference is that the civilian barrel has a shorter leade, and the rifling begins closer to the chamber. This can lead to higher pressures, it is said.

However, it is common for serious target shooters to seat the bullet to within a few thousandths of an inch from the lands, so I don't understand that alleged problem.

About forty years ago I loaded some .243 rounds with the bullets not seated deeply enough and I didn't realize it. No problems showed up in a five-shot string; nice tight group as was expected. I loaded a sixth round and then changed my mind about shooting it. When I retracted the bolt to remove the cartridge, the bullet stayed slightly stuck into the lands. No pressure signs on the primers.

As far as relative chamber pressures, I can only note that the lugs of a bolt-action rifle have more cross-sectional area than the lugs on an AR, and thus are stronger in resisting rearward force upon firing. For a chamber pressure of 50,000 psi, the rearward force is about 4,800 pounds.

However, there are many pages of factory and other warnings against shooting GI ammo in civilian chambers...

DaveInPA · August 7, 2009, 08:22 PM

5.56 NATO is a higher pressure round than the civilian loading, the .223 Remington. Do not shoot 5.56 in a .223 chamber. Shooting .223 in a 5.56 chamber is fine.

This is why whenever I buy or build an AR, I make sure the barrel has either a 5.56 or a .223 Wylde chamber. (5.56 is good to go in a Wylde chamber)

GeauxTide · August 7, 2009, 08:32 PM

I've got a .223 Bolt gun and wouldn't worry about 55gr military ammo; however, I wouldn't shoot 62gr or heavier military stock because of the throating and the slower rifling twist. I guaranteed that my top load, which is not maximum, propelling a 55gr NBT at 3300 is over 50,000cup.

Double J · August 8, 2009, 12:13 AM

The 5.56x45mm NATO is a nice European metric designation for what we call the .223 Remington.
On a par with referring to a 7.62x51R as the .30-30 Winchester.
And then there's the confussing aspect of the .223 Remington cartridge not being .223 anyway, because it has a .224 bullet.

DaveInPA · August 8, 2009, 05:44 AM

Double J, like I said it's more than just a different name. 5.56 NATO is loaded to higher chamber pressures than .223 Remington . . .

Palmetto-Pride · August 8, 2009, 06:48 AM

I am usually not one to point out a topic that has been covered time and time again, but on this one I must, if you just use the search function you will come up with all the 5.56 vs .223 you can stand here is a recent one.

http://www.thefiringline.com/forums/...ight=5.56+.223

Double J · August 8, 2009, 09:25 PM

Doubtfull that Nato loads are nearly as hot as some of our varmint loads. Their velocities sure are much slower. I suspect that most civilian-market ammo is down loaded for liability reasons.

KyJim · August 8, 2009, 10:12 PM

Double J -- It's not that simple. The 5.56 may have higher pressures and lower velocities than .223. See post 2 above.

Double J · August 9, 2009, 10:37 AM

The 5.56mm NATO is proof tested to 430MPa (62,366 psi).
The .223 Remington is proof tested by SAAMI to a lower pressure of 379.21 MPa (55,000) psi.
C.I.P. " defines the maximum service and proof test pressures of the .223 Remington cartridge equal to the 5.56 NATO."
Not so much the cartridge, but the chambers of a particular firearm designed to handle specialized length bullets. Longer bullets are heavy bullets. That in it's self increases chamber pressure. Mil- spec brass is thicker and has less internal capacity than commercial brass. Outside demensions are the same.

Art Eatman · August 9, 2009, 11:50 AM

DoubleJ, you might think about this comment, "Longer bullets are heavy bullets. That in it's self increases chamber pressure."

For example, I don't think that factory loads (or handloads) with 200-grain bullets in an '06 increase chamber pressure over 110-grain bullets.

Heavier bullet = less powder = equal pressures.

Double J · August 12, 2009, 09:46 PM

5.56 with less internal capacity, same bullet, same powder= more compressed load= higher pressure .
Longer bullet, seated to same OAL, with same powder charge= even more pressure. Only way to "cheat" is to lengthen OAL. And that requires more leade. Again, that's getting back to a specialized chamber for a specific load.
The Wylde(Rock River Arms) takes advantage of the longer bullets by useing a specific chamber design. It's not NATO specific by the way. The same custom work can alter any .223 to shoot those long custom bullets.
The original question was about the cartridges. In the 55 grain bullets, case thicknesses are the major factor. The differences between brand name ammo is probably greater than what we are discussing here.

August 7, 2009, 07:27 PM	#1
JRDANIELS Member Join Date: July 3, 2009 Location: Wyoming Posts: 43	5.56mm & .223 Remington Whats the real story? Exact same? 5.56 has a little thicker case? Never understood the actual differance. Whats the real story here? And, is it ok to fire 5.56mm ammo in a .223 chamber and also ok to fire .223 in a 5.56mm chamber?

August 7, 2009, 08:32 PM	#4
GeauxTide Senior Member Join Date: April 20, 2009 Location: Helena, AL Posts: 4,424	+1 Art Eastman I've got a .223 Bolt gun and wouldn't worry about 55gr military ammo; however, I wouldn't shoot 62gr or heavier military stock because of the throating and the slower rifling twist. I guaranteed that my top load, which is not maximum, propelling a 55gr NBT at 3300 is over 50,000cup.

August 8, 2009, 12:13 AM	#5
Double J Senior Member Join Date: February 12, 2007 Location: So. Illinois Posts: 547	The 5.56x45mm NATO is a nice European metric designation for what we call the .223 Remington. On a par with referring to a 7.62x51R as the .30-30 Winchester. And then there's the confussing aspect of the .223 Remington cartridge not being .223 anyway, because it has a .224 bullet. Last edited by Double J; August 8, 2009 at 12:21 AM.

August 8, 2009, 06:48 AM	#7
Palmetto-Pride Senior Member Join Date: May 31, 2009 Location: Charleston, SC Posts: 2,071	I am usually not one to point out a topic that has been covered time and time again, but on this one I must, if you just use the search function you will come up with all the 5.56 vs .223 you can stand here is a recent one. http://www.thefiringline.com/forums/...ight=5.56+.223 __________________ “The problem with socialism is that you eventually run out of other people's money.” -Margaret Thatcher-

August 7, 2009, 07:48 PM	#2
Art Eatman Staff in Memoriam Join Date: November 13, 1998 Location: Terlingua, TX; Thomasville, GA Posts: 24,798	As near as I can tell from the numberous articles and discussions, the primary difference is that the civilian barrel has a shorter leade, and the rifling begins closer to the chamber. This can lead to higher pressures, it is said. However, it is common for serious target shooters to seat the bullet to within a few thousandths of an inch from the lands, so I don't understand that alleged problem. About forty years ago I loaded some .243 rounds with the bullets not seated deeply enough and I didn't realize it. No problems showed up in a five-shot string; nice tight group as was expected. I loaded a sixth round and then changed my mind about shooting it. When I retracted the bolt to remove the cartridge, the bullet stayed slightly stuck into the lands. No pressure signs on the primers. As far as relative chamber pressures, I can only note that the lugs of a bolt-action rifle have more cross-sectional area than the lugs on an AR, and thus are stronger in resisting rearward force upon firing. For a chamber pressure of 50,000 psi, the rearward force is about 4,800 pounds. However, there are many pages of factory and other warnings against shooting GI ammo in civilian chambers...

August 7, 2009, 08:22 PM	#3
DaveInPA Senior Member Join Date: January 20, 2008 Location: Berks County, PA Posts: 1,106	5.56 NATO is a higher pressure round than the civilian loading, the .223 Remington. Do not shoot 5.56 in a .223 chamber. Shooting .223 in a 5.56 chamber is fine. This is why whenever I buy or build an AR, I make sure the barrel has either a 5.56 or a .223 Wylde chamber. (5.56 is good to go in a Wylde chamber)

August 8, 2009, 05:44 AM	#6
DaveInPA Senior Member Join Date: January 20, 2008 Location: Berks County, PA Posts: 1,106	Double J, like I said it's more than just a different name. 5.56 NATO is loaded to higher chamber pressures than .223 Remington . . .

August 8, 2009, 09:25 PM	#8
Double J Senior Member Join Date: February 12, 2007 Location: So. Illinois Posts: 547	Doubtfull that Nato loads are nearly as hot as some of our varmint loads. Their velocities sure are much slower. I suspect that most civilian-market ammo is down loaded for liability reasons.

August 8, 2009, 10:12 PM	#9
KyJim Senior Member Join Date: July 26, 2005 Location: The Bluegrass Posts: 9,142	Double J -- It's not that simple. The 5.56 may have higher pressures and lower velocities than .223. See post 2 above.

August 9, 2009, 10:37 AM	#10
Double J Senior Member Join Date: February 12, 2007 Location: So. Illinois Posts: 547	The 5.56mm NATO is proof tested to 430MPa (62,366 psi). The .223 Remington is proof tested by SAAMI to a lower pressure of 379.21 MPa (55,000) psi. C.I.P. " defines the maximum service and proof test pressures of the .223 Remington cartridge equal to the 5.56 NATO." Not so much the cartridge, but the chambers of a particular firearm designed to handle specialized length bullets. Longer bullets are heavy bullets. That in it's self increases chamber pressure. Mil- spec brass is thicker and has less internal capacity than commercial brass. Outside demensions are the same.

August 9, 2009, 11:50 AM	#11
Art Eatman Staff in Memoriam Join Date: November 13, 1998 Location: Terlingua, TX; Thomasville, GA Posts: 24,798	DoubleJ, you might think about this comment, "Longer bullets are heavy bullets. That in it's self increases chamber pressure." For example, I don't think that factory loads (or handloads) with 200-grain bullets in an '06 increase chamber pressure over 110-grain bullets. Heavier bullet = less powder = equal pressures.

August 12, 2009, 09:46 PM	#12
Double J Senior Member Join Date: February 12, 2007 Location: So. Illinois Posts: 547	5.56 with less internal capacity, same bullet, same powder= more compressed load= higher pressure . Longer bullet, seated to same OAL, with same powder charge= even more pressure. Only way to "cheat" is to lengthen OAL. And that requires more leade. Again, that's getting back to a specialized chamber for a specific load. The Wylde(Rock River Arms) takes advantage of the longer bullets by useing a specific chamber design. It's not NATO specific by the way. The same custom work can alter any .223 to shoot those long custom bullets. The original question was about the cartridges. In the 55 grain bullets, case thicknesses are the major factor. The differences between brand name ammo is probably greater than what we are discussing here.