View Full Version : 223 vs 5.56

11-04-2009, 12:16 PM
I have read lots on the issue of using 223 Remington and 5.56 military ammo, but a question remains.

I know 5.56 military runs at a higher pressure. But, this is an AR15 rifle so it is certainly strong enough for military pressure. But, perhaps not, if the high pressure military pressure is boosted even higher by the bullet running into a short chamber lead (223 Remington). Is the really the crux of the matter?

I know 5.56 is loaded to a higher pressure, but how? Reduced case volume due to thicker walls, more powder, deeper seated bullet, or...? I ask because I ordered BlackHills remanufactured 223 Remington ammo for my AR15 chambered in 223, and I now find out that the BlackHills ammo may be using military brass (reduced interior volume).

Explanations welcome!

- Phil

11-04-2009, 12:24 PM
You've pretty much answered your own question. It's mostly (from what i've found) due to the short chamber lead. A 5.56 in a .223 barrel with contact the rifleing sooner...but just barely. That is also why some barrels can be worn out faster by using 5.56 in a .223 rifle. I've also found that some manufacturers will use 5.56 brass with an actual .223 bullet; probably because they get spent cases from the military too. Pretty much everything you've mentioned will generate a higher pressure....so i guess the real answer is that it depends on the manufacturer and what combo of those factors their using in their ammo. My suggestion, dont use 5.56 in a .223 unless you have a VERY SOLID barrel (and overall gun).

11-04-2009, 12:25 PM
5.56mm has a longer leade and the powder is hotter than .223 powder. The thicker walls are needed for the higher pressures. The leade in a 5.56mm is almost exactly double the leade in a .223. The short leade of a .223 in a 5.56mm isn't dangerous but it isn't the most accurate. The longer leade of a 5.56mm and the higher pressures is dangerous in a .223 chamber.

gun toting monkeyboy
11-04-2009, 12:28 PM
If the manufacturer says it is .223, that means they have sized it to .223 dimensions, and the load falls within the .223 pressure envelope. It will be safe in your .223 rifle. As for how 5.56 is loaded hotter, you have the increased thickness of the military brass reducing the internal capacity, and they load it up with hotter powder charges. That's about the only difference.

11-04-2009, 12:32 PM
I'm not as 'gun techy' as I wouold like to be butI believe you have it atlest somewhat correct.
I had done some digging before buying my 5.56 and I thaught it was dumb how some gun sales people say there is no difference and some say that shooting .223 in a gun made for 5.56, the .223 will be less accurate.
unless you want to distroy your weapon.

But I'm sure I'll get reamed and told I am totaly wrong. In that case My bad.
If only all gun sales people actually knew the facts of what they are selling:eek:.

11-04-2009, 12:49 PM
From more research, it appears that the bullet on 5.56 can literally be jammed into the rifling lands. That, combined with the higher pressure of the 5.56, would generate a substantial pressure spike. Not good.

Still, I wondered how a 5.56 round could jam into the 223 rifling when these rounds could only be only so long given they have to fit in the mag, especially, when 223 people are single loading even longer bullets into the 223 and they are NOT jamming the lands. Apparently, from what I can gather so far, it is due to the bullet profile. Don't quote me on this, but what really matters is the case to ogive length, and 5.56 may be quite long in this regard, too long to fit in a 223 chamber without jamming the lands.

I also learned that the military use a long lead to build velocity, and while this arrangement may hurt accuracy, the velocity took precedence.

Alright, let me know if I got any of this wrong.

- Phil