What's the difference . . .

[Gunplummer]

Again, I do not care what your position is on chamber specs as it came from bad information. SAAMI did not draw the specs for the military. I think Frankford arsenal knew what it was talking about. Putting up a smoke screen of information that does not pertain to the topic has no affect on a guy that has made chamber reamers from prints, from castings, fired brass, and the occasional wildcat. Some body explain to me how you can have thicker brass but not affect the neck diameter in the chamber? Military 30.06 and .308 brass has been known to be tight in civilian guns at the neck area. A lot of reloaders used to shave or ream the necks to thin it out. It is possible to use thicker brass and just have less case volume and basicly the same O.D. It is not possible to do that at the neck. It does not take much before you have a bad seal, especially with heavier brass, so the military chamber neck size is not overly large for the case that was intended for it.

[Unclenick]

Gunplummer,

I think I've solved the neck turning issue you mentioned. I'm assuming you were referring to .308/7.62 when you mentioned you remembered fellows having to turn military necks thinner. I got hold of a copy of the declassified STANAG 2340, edition 3, Annex sheets 1-4 and Annex B (chamber) drawings of the 7.62 NATO cartridge. The maximum case dimensions are identical to the SAAMI spec, exactly as Sellier & Bellot said. The NATO drawings also use the modern 0.400 inch shoulder datum (see below) for headspace, rather than the old method of breech face to body/shoulder intersect. This change was made because it gives a common diameter to case and chamber shoulders, where the old method, because the case is narrower than the chamber, has a longer number for the case than for the chamber. Also, it eliminates having to guess where the intersect lies inside the chamber metal when that corner has its allowed radius, and where it is in the air outside the case when the case body/shoulder corner has its allowed radius.

There is one significant and two minor differences in the NATO and SAAMI specs. The important one (to my mind) is the NATO design specifies brass hardness test numbers at specific locations on a sectioned case head and along locations on the case, while SAAMI leaves that to the manufacturer's discretion. That accounts for why NATO spec brass holds up better in self-loaders; its hardness is controlled. The two minor ones are that the SAAMI tolerance for finished cartridge COL allows for shorter cartridges than NATO does, and the SAAMI case length to the headspace datum diameter on the shoulder is 1.634" -0.007", while NATO uses 1.634" -0.006". So the NATO minimum case is 0.001" longer than the SAAMI minimum length case.

Of particular interest to the neck turning issue that the NATO maximum finished cartridge neck diameter over the bullet in a finished cartridge is the exact same 0.3435" that SAAMI specifies. That means the NATO case will fit any standard SAAMI minimum diameter chamber with 0.0007" clearance to spare at the neck, because the SAAMI neck mouth is 0.3442" minimum.

The problem comes with match chambers. Match chambers are smaller in neck diameter than the SAAMI standard chamber. The Clymer reamer specs show the M14/M1A match reamer for Lake City M852 match ammo has a case mouth diameter of 0.3430", half a thousandth too small for either a NATO or SAAMI maximum case necks. Palma Match chambers are even smaller at 0.3400". But Lake City never made M852 necks that thick. The spec allows necks as thick as 0.0175", but Lake City, like commercial manufacturers, made M852 brass necks about 0.0155" thick on average (their extra thickness is all near the head). Over the Sierra .308" diameter 168 grain MatchKing, that's an outside neck diameter of 0.339". So M852 not only fit the special M852 match chambers, but they'd fit the Palma match chamber, too. But bring in some foreign made NATO ammo, or possibly even some non-Lake City domestic NATO ammo with 0.016" to 0.0175" necks, and suddenly the match chambers won't let them in.

Bottom line: It's the chamber specs and not the cartridge specs, unless the cartridges were out of spec. That's also possible. Read through this document until you get to 7.62 information.

[JRLSH]

OK, forgive my ignorance then. According to another post you should not shoot 5.56 ammo in a .223 barrel. What will happen if you inadvertantly do? Will it ruin the barrel? Or is it a matter of case size? Sorry if this question seems stupid...

[Unclenick]

What will happen is it will shoot. The peak pressure spec is higher for 5.56 NATO than for U.S. commercial ammo, but not as high as the proof load spec for commercial firearms chambered in .223 Rem. Also, the Europeans load their 5.56 and .223 to the exact same 62,366 psi MAP and commercial guns handle their .223 Rem just fine and you can buy that ammo here; Sellier & Bellot, Norma, and Lapua ammo are examples. No special warnings exist against using those come from any gun makers. US commercial .223 Rem ammo is loaded to the lower SAAMI 55,000 psi MAP spec, which will make throats last longer, but I've never seen a warning to use only domestic ammo in an American made .223 firearm, either.

Bottom line, no problem with shooting 5.56 in .223 has ever come to my attention, except where it turns up in some folk's imaginations.

[riggins_83]

Generally 5.56 runs at a higher pressure and headspacing spec for 5.56 is a bit longer than 223 rem.

[Mike-Mat]

Here's the dimensions for both cartridges. They are exactly the same.

223
http://en.wikipedia.org/wiki/File:.223_Remington.jpg

5.56
http://en.wikipedia.org/wiki/File:5.56x45mm_NATO.jpg

If you toggle between those 2 drawings, You'll see they are exactly the same.

Mike

[Gunplummer]

This change was made, that change was made, Yada-Yada-Yada. There was a change. Yes, NOW everybody claims to be in sync. I don't really care as I do not shoot surplus ammo any way.

[wncchester]

For reloaders the effective difference between '5.56' and '.223' is the pressure when the bullet passes the gas port on autoloaders.

[Unclenick]

Mike,

Those Wiki drawings appear to show different radius specs for the corners of the shoulder with the neck and body. Neither is an official drawing, though, and they lack the tolerance specs. After getting hold of the STANAG drawings for the 7.62, I've not yet got them for the 5.56, as it appears they may still be classified (the government site I used for the 7.62 drawings doesn't let me at the 5.56 drawings). I'll have to verify if that's the case or not (no pun intended). But I don't see a reason they'd be different any more than the 7.62 turned out to be.