.223 REM vs. 5.56 NATO loads

[nixdorf]

I'm interested in the difference between .223 Remington and 5.56 NATO from a reloading perspective.

I understand the difference is primarily cartridge pressure. From what I've read, a .223 REM chambered rifle is only good to shoot .223 REM, but a 5.56 NATO rifle can fire either .223 or 5.56.

Given that, what is the real difference? I've only ever found loading data for .223 Remington in the three reloading data books I own and in online searches. I would have expected to find 5.56 NATO load data that is similar to .223 Remington, but with higher pressures (either by more powder, lower COAL, or something else).

 

[Afy]

Here in Europe we shoot .223 rem and 5.56 ammo interchangeably from our .223 rem guns, which generally are 5.56 in reality.

 

[Clark]

There is so much safety margin in the guns and the brass of a 223 or 5.56 compared to the registered max average pressure, that worrying about the difference for hand loading for you own rifle, is about as productive as talking about how many angels can dance on the head of a pin.

 

[243winxb]

Factory Nato 5.56mm ammo should not be fired in a 223 rem chanber, because the Nato will produce high pressure. See SAAMI site. The both load the same, start low on the powder charger and work up as always. INfo on chanbers here > http://www.6mmbr.com/223Rem.html On this site, Sierra lists separate load data for autos & bolt actions.

 

[Grumulkin]

Just curious. Has ANYONE personally had "factory" 5.56 NATO ammo cause high pressure in a gun chambered for the allegedly different 223 Remington cartridge? I have a whole box of Federal Lake City stuff that shoots just fine in my 223 Remington with no signs of high pressure.

 

[bigedp51]

The chamber pressures for the .223 and 5.56 are the same, the confusion is created because the military measures chamber pressure differently than the SAAMI. The difference is how the rifles are throated and what bullet weight you are shooting. I have a Stevens 200 with a 1 in 9 twist which is throated longer for heavier bullets, and a rifle with a 1 in 12 twist will have a shorter throat.

Please note the European CIP the counter part to the American SAAMI rates the .308/7.62 and .223/5.56 as the same cartridge at the same pressure.

 

[Cypress]

The only relevant concern IMO is that 5.56 brass often has thicker walls thus less case capacity thus higher pressure. This is only a real concern when loading to the ragged edge which I do not do anyway. Barnes data for the TSX bullets had .223 and 5.56 NATO loads.

 

[Grumulkin]

The only relevant concern IMO is that 5.56 brass often has thicker walls thus less case capacity thus higher pressure. This is only a real concern when loading to the ragged edge which I do not do anyway. Barnes data for the TSX bullets had .223 and 5.56 NATO loads.

I use to think 5.56 NATO brass was thicker but, after seeing this subject hashed out ad nauseam before I no longer think so. I do know, however that military 30/06 and 308 brass is thicker from personal experience.

Hornady also lists .223 and 5.56 loads but I believe the reason is that usually 5.56 loads are to be shot in AR-15 rifles and certain loads work better for them and not because of any pressure concerns.

 

[bigedp51]

1 in 12 twist uses bullets from 40 to 60 grains. (lighter bullets)



1 in 9 twist uses bullets from 68 to 75 grains. (heavier bullets)



The "ONLY" difference is the bullet weight, throating and barrel twist rate. The twist rate for the .223 and M16A1 were the same at 1 in 12 and had "NO" pressure differences. With the modification to the M16A2, the 1 in 7 twist, longer heavier bullets and "longer" throating the ammunition was no longer interchangeable without pressure spikes.
M16A1 = 1 in 12 twist
M16A2 = 1 in 7 twist
M16A4 = 1 in 7 twist

 

[Dapperdan]

We are shooting 223 in a Remington 700 with 1 in 12" twist. The rifle says 223 Remington on the barrel. We don't use anything but reloads, trimmed the same length, so I guess the only issue would be case capacity? Lots of NATO spec brass to pick up at the range, but I just don't like messing with the primer crimp, so we use just 223 Remington commercial cases. If the milspec brass is thicker, I would think that pressures would be higher, given the same powder charge. There is some difference in capacity among the manufacturers, it is obvious when you visually inspect powder charges in different brands of cases. I'll stick with 223 Remington commercial cases, anything with a primer crimp is suspect, to me. Take care and thank ya!

 

[nixdorf]

Wow, that's a lot of really good info you folks shared.

I think I'm going to dig up some heavier-grain bullet loads for my Smith and Wesson M&P-15 (1 in 9 twist). I've been shooting 55 grain bullet reloads lately which seem to be a bit on the light side for that twist rate.

Thanks a ton!

 

[243winxb]

I have a whole box of Federal Lake City stuff that shoots just fine in my 223 Remington with no signs of high pressure.

Does it have the NATO headstamp?

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