This argument is as old a the round itself. Technical matters aside the difference is academic, I have used various brands of .223 Rem and a few Radway Green and German 5.56 in my Remington bolt action and my Mini 14. The latter eats anything and everything no problems; the Remington however because of its slow twist (1 in 12) did not like the miltitary stuff and spread it all over the place. I have reloaded RG cases for my Remington using 52grn bullets and had excellent results, the only difference there is that military cases tend to be thicker and heavier than civvy cases, which means you have to watch out just how much powder you put in the military cases.
I really wish people would stop posting american doonsayers bollocks and urban myths about the ammo. The round is one and the same at 55 graiin loading as originally issued. The US civilian shooters after WW2 were led down the path that anything in mm (ergo military) is bad so everything must be in inches. Not a problem. the real issues are when people use brass with different case wall thickness in their little AR and wonder why it overpressures (got to go some to blow primers in those little cases) when shoving uncle Bubbas latest supersonic at 1200 yards pet handload doesnt have proof laws, it has lawyers, it likes to print stupidly long written warnings on everything possible including the firearms themselves.
I can give you two identical loads in that calibre which are different in America but as we are talking calibre not ammunition load then the OPs statement is utter bollocks!
In fact if you read the whole premise is all about leades which are tolerance variations in chamberings not calibres and vary between rifles of the same factory and can be specified if wished. More bollocks
these days you can get chambering reamers that are between the .223 and 5.56mm chamber throat profiles,
so in this day and age, no, theres is no real diff between the two.
The 5.56mm NATO chambering, known as a NATO or mil-spec chamber, has a longer leade, which is the distance between the mouth of the cartridge and the point at which the rifling engages the bullet. The .223 Remington chambering, known as SAAMI chamber, is allowed to have a shorter leade, and is only required to be proof tested to the lower SAAMI chamber pressure. To address these issues, various proprietary chambers exist, such as the Wylde chamber (Bill Wylde) or the ArmaLite chamber, which are designed to handle both 5.56mm NATO and .223 Remington equally well. The dimensions and leade of the .223 Remington minimum C.I.P. chamber also differ from the 5.56mm NATO chamber specification.
To keep it simple over here. Ya don't put your surplus nato ammo in your dad's old .223 with a 1/10 or 1/12 twist. It has a shorter neck on her and you will over pressure the rifle. You can spray as much .223 down range out of your M16A2 nato rifle as you want. It wont hurt her.
My hunting buddy has a surprisingly accurate stainless steel savage. I doubted the accuracy of his .223 stamped rifle and couldn't figure out how it shot so well. It was 1/10 23in crowned and he would intentionally over pressure the barrel with xm-80 military ammo. The newer rifles can usually take the over pressuring. You wouldn't want to trust the steel of an old ruger M/77 bolt action with 5.56. Your primers would blow right out the ass end.
The 5.56 nato round was designed to wound the enemy and deplete their resources. It's a worthless and dangerous piece of trash that should be removed from service. I've hit things that keep running after a direct center mass shot. F***ing worthless puncture wound round.
I now use them only for killing ground squirrels out in the pastures. It's only good for a target rifle.
Much as I have issues with how the 5.56/.223 has been employed, it is a capable round when used and loaded correctly. In fact its flexibility is something of an asset when reloading for very specific situations, however the 'one load fits all' scenario does not work. As for the old chestnut of being designed to wound, well any bullet which is long in relation to its diameter, keeping its CofG to the rear, will keyhole when hitting a deep enough tgt. Its simply a fact of design but a potentially useful one.
Marc basically yes Winchester pissed of the US arms trade by releasing the T65 cartridge as .308 win thus getting its name out there attached to surplus ammo, cheap beass and the US civi shooters fave the latest chambering! The two rounds when first issued are the same as are the chamberings but shock horror now you can get custom throats reamed and therefore according to SAAMI they are different. It mostly now stems from the US lagging behind Europe with bullet design in the .22 range during rhe 70's and the NATO trials!
Nothing to worry about as factory 556 goes great out of my 1 in 12 Ruger and doesn't overpressure!
The 5.56/.223 and the 7.62/308Win debates amuse me slightly. Due to the wonders of German firearms legislation the military calibres 7.62 and 5.56 are no no for civvies. Therefore the ex military ammo I aquire is all over stamped 308Win or .223 Rem as appropriate. The civilian versions of military rifles, predominantly AR15 and clones unlimited, are therefore sold as the civilian equivalent calibre. My L1A1 is entered on my licence as a 308Win calibre semi auto rifle. Amazingly enough my L1A1 eats military ammo even though it is officially classed as 308Win; Lake City, ex Bundeswehr ammo, RG, and other unidentified 7.62 all disappear downrange and hit the tgt. Even more amazing the civvy ammo and my reloads do the same! Same deal for my .223 Rem weapons. As previously stated any difference is largely academic.
More accurate to say it is used because it often wounds if non vital organs are hit but obviously kills if they are.
In addition the 5.56 is around 50% smaller in volume than a 7.62 so in theory you can carry double the rounds.