.223 vs 5.56

[ILostMyGoat]

Hey guys let me preface saying I did do a search before posting. But adequate results were not found. I understand the relationship between these two rounds but I just want to confirm a .223 die set from RCBS will work properly to reload 5.56. Thanks for the input


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[M-Tecs]

yes no issues. Case dimensions are the same.

[Larry Gibson]

M-Tecs is correct. If you are loading for a gas gun that does not have a tight match chamber (milspec in other words) then I suggest you use RCBS standard .223 X-dies. You will get longer case life and will not have to trim the cases after each FL sizing.

FYI; while the cases are the same dimension factory 223 are loaded not to exceed the SAAMI MAP of 55,000 psi. Most recent manual data also adheres to that same MAP. The US nor NATO do not load to SAAMI specs. I have measured the pressure of numerous different 223/5.56 rounds. Older M193 (pre Afghanistan/Iraq war) ran 55 - 60,000 psi. Newer (since about 2004) M193 and M855 rounds run 60 - 64,000 psi. Be advised I measured those pressures in a minimum spec 223 chamber.

Thus, the unknowing will fire 5.56 in 223 chambers and shout to high heaven the pressure is greater. Ergo, it must be the chamber that makes 5.56 in a 223 chamber have higher pressure...... when the fact is the 5.56 rounds probably gave higher pressure to begin with. In modern locked breech action rifles shooting 5.56 in the "223 Remington" poses no risk to rifle. If used in a break open I suggest sticking to SAAMI MAP pressures. Also match the bullet to the barrel twist. If you and a 12 or 14" twist then M193 (55 gr FMJBT) will work fine. Shooting hevier bullets will simply result in inaccuracy or non accuracy because the bullet (heavier than 55 gr) won't stabilize. If a 9 0r 10" twist then bullets up through 69 gr can be used. If 7-8" twist then just about any bullet can be used.

[45_Colt]

What others have posted about the case dimensions being the same between .223 and 5.56 is true. So you can use the .223 case sizing die for a 5.56 load.

However, the chambers are different between the two cartridges. So care must be taken here. The 5.56 chamber has a longer & larger diameter throat, which is required due to the 5.56 loads. Use a factory 5.56 cartridge in a true .223 chamber and high pressures can/will result.

The opposite can be done, using a .223 factory round in a 5.56 chamber with no ill pressure issues.

To further throw some wrenches into the mix, some rifles listed as .223 have the longer throat and can safely use a 5.56 round. Many of the Ruger Mini-14 rifles are this way (please do a serial number look up to see if your particular Mini is OK in this regard).

45_Colt

[ILostMyGoat]

Awesome info thanks guys! I didn’t know the pressure variety was such a spread


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[Rapidrob]

The original M-16 Manual for the USMC says " caliber .223 Remington / 5.56 mm" and that was 1964. The lead in the chamber for automatic fire is the difference. It is not the same as .308 Winchester / 7.62x51mm problems with case capacity and chamber pressure.

[Drew P]

So are we saying 5.56 brass is in fact identical to 223 in all ways?

[M-Tecs]

So are we saying 5.56 brass is in fact identical to 223 in all ways?

Within manufacturers specs yes. Externally the are the same. Chambers and throats not so much.

[Winger Ed.]

So are we saying 5.56 brass is in fact identical to 223 in all ways?

In addition to what's been said, the wall thickness of GI brass is noted to be thicker.
New manuals don't mention it, but older ones did. They recommended to ease off about one grain
of powder to compensate for it and keep the pressure within the safety zone and be close to the listed speed.

[Drew P]

In addition to what's been said, the wall thickness of GI brass is noted to be thicker.
New manuals don't mention it, but older ones did. They recommended to ease off about one grain
of powder to compensate for it and keep the pressure within the safety zone and be close to the listed speed.

That’s what I had thought, thanks

[M-Tecs]

With 308 and 30/06 there was a volume difference. With .223/5.56 not so much.

https://www.accurateshooter.com/cartridge-guides/223rem/

[Winger Ed.]

That’s what I had thought, thanks

.223/5.56 has a interesting history of development.

What I've sort of gathered is the military adapted the .223 varmint cartridge with a 50, then a 55gr FMJ in the early days to the M16.
I've got a old SP1 series Colt AR from the 70's. Its barrel is stamped .223, and I think it has a 1:12 twist.

As time went on, the M16/AR platform got modified and improved about as much as the Chevy small block V8.
Barrel twist went to 1:10, then to 1:7 as the bullets for it got heavier and heavier.

If you have a modern generation AR, it'll shoot almost anything listed as .223 or 5.56 that can handle the twist rate.
Thin jackets like Hornady SX series will probably fly apart in flight from the high rotation,
and people have said thin jacket bullets can/will shatter from hitting rain drops.

With an old school .223Rem, a lot of them wouldn't chamber a GI 5.56, but still I'd go easy with GI type 5.56 ammo.
They might chamber, but usually aren't very accurate, and there is the higher pressure to be concerned with.

[Drew P]

.223/5.56 has a interesting history of development.

What I've sort of gathered is the military adapted the .223 varmint cartridge with a 50, then a 55gr FMJ in the early days to the M16.
I've got a old SP1 series Colt AR from the 70's. Its barrel is stamped .223, and I think it has a 1:12 twist.

As time went on, the M16/AR platform got modified and improved about as much as the Chevy small block V8.
Barrel twist went to 1:10, then to 1:7 as the bullets for it got heavier and heavier.

If you have a modern generation AR, it'll shoot almost anything listed as .223 or 5.56 that can handle the twist rate.
Thin jackets like Hornady SX series will probably fly apart in flight from the high rotation,
and people have said thin jacket bullets can/will shatter from hitting rain drops.

With an old school .223Rem, a lot of them wouldn't chamber a GI 5.56, but still I'd go easy with GI type 5.56 ammo.
They might chamber, but usually aren't very accurate, and there is the higher pressure to be concerned with.
Interesting, I had not ever read about that and I have a book dedicated to the loading of 223 for ar15. Maybe it is in there, I forget a lot these days.

[rbuck351]

My wife bought me one of the first Rem 700 V rifles in 223 forty some years ago. I have shot about 1500 military 5.56 rounds through it. It has a 1/12 twist and accuracy goes away with bullets over 55gr. The 5.56 ammo I used in it was all 1970s 55gr and never showed any pressure problems. I have never tried any of the newer 5.56 ammo as it uses heavier bullets. When I first got the rifle, 223 ammo was rare so I used 5.56 brass and started low and worked up to normal max loads without any signs of pressure. I don't know if the 62gr 5.56 ammo will chamber in my rifle as it may have a shorter lead. I quit using military brass many years ago when 223 brass became much easier to find but other than the crimped primer I haven't noticed any difference in performance.