What accuracy can I expect shooting .223 in a 5.56 chambered AR?

T

TruthTellers

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Brownell's had a 10% off coupon and free shipping on top of a sale on some Federal ammo, who currently has a rebate of 3 cents/rd for .223 and 5 cents/rd for 5.56 ammo... so I bought a lot of ammo. 500 rds of 62 grain XM855 and 450 rounds of 55 grain.

What I overlooked was the 55 grain ammo was .223, not 5.56. I think they were sold out of any 55 grain 5.56 ammo, which is why I ended up with .223.

I know it's okay to shoot .223 in a 5.56 chambered rifle, but not vice versa, but I'm wondering what can I expect in terms of accuracy doing that?

This is mostly going to be for plinking and testing to see if my AR prefers 55 to 62 grain bullets. Also, I have a .223 chambered H&R single shot, so if the accuracy is poor, I have a spare rifle to shoot it in.
 
You didn't buy the most accurate ammo made, but the fact that it is 223 instead of 5.56 won't make any difference at all. The external case dimensions are exactly the same. 5.56 CAN be loaded a little hotter, but in the real world usually isn't. For all practical purposes the 2 are interchangeable.
 
I know neither XM193 or M855 are super accurate ammo, but I bought them to test as a control or baseline of accuracy when I try different ammo in the future.
 
I had some green tip back when I had an AR that was not bad.

1.5 inches as I recall. It was as good as any of my hand-loads.
 
You failed to mention your twist rate of your barrel which is the more important question than 5.56 vs .223. The heavier rounds function better with a faster twist ratio, 1:7 or 1:9 vs 1:10 or slower for 55 gr bullets and smaller.

Any way you look at it you will have to re-zero for best accuracy when changing manufacturer and bullet size.
 
About all I can do is say that this;
jmr 40
You didn't buy the most accurate ammo made, but the fact that it is 223 instead of 5.56 won't make any difference at all. The external case dimensions are exactly the same. 5.56 CAN be loaded a little hotter, but in the real world usually isn't. For all practical purposes the 2 are interchangeable.
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and this:
MTT TL
You failed to mention your twist rate of your barrel which is the more important question than 5.56 vs .223. The heavier rounds function better with a faster twist ratio, 1:7 or 1:9 vs 1:10 or slower for 55 gr bullets and smaller.
Click to expand...

That pretty much sums things up. Most of the 5.56 stuff I have bought shoots pretty well in any of my AR rifles, pretty well but not great meaning depending on rifle and twist I may see 2 MOA on a good day at 100 yards. My best results come with rolling my own 223 Remington.

Ron
 
MTT TL said:
You failed to mention your twist rate of your barrel which is the more important question than 5.56 vs .223. The heavier rounds function better with a faster twist ratio, 1:7 or 1:9 vs 1:10 or slower for 55 gr bullets and smaller.

Any way you look at it you will have to re-zero for best accuracy when changing manufacturer and bullet size.
Click to expand...
Twist is 1:8, I believe. It's a Faxon gunner barrel.
 
With a 1:8, the consensus is that shooting 62-78gr bullets should offer great accuracy. 55gr and bullets with less surface area less so. You might shoot it and everything turns out great.

Also keep in mind that 62gr green tip is not exactly known for tack driving performance. There is better stuff out there.
 
"....223 in a 5.56..." That has nothing to do with accuracy. Your rifle will either like the ammo or it won't.
Military ammo isn't loaded for great accuracy. It's loaded to be reliable out of rifles or MG's.
And before there was an internet, .223 and 5.56 were the same thing. Literally millions of rounds have been fired out of battle rifles and commercial hunting rifles with no fuss.
 
When it comes to Federal 55 grain FMJ ammunition, I find little or no difference in accuracty between that head stamped .223 Rem and the XM193 5.56 mm with the NATO head stamp. I have three ARs, one with a 16" 1:8 twist, 5.56 NATO-chambered barrel, one with a 16" 1:7 twist, NATO-chambered barrel, and one with an 18" 1:7 twist, 223 Wylde-chambered barrel.

I agree with jmr40. Even though 5.56 ammunition is sometimes loaded slightly hotter than .223 Remington, it often is not, or not enough to affect accuracy. Any decent barrel with a twist rate from 1:7 to 1:12 will stabilize 55 grain FMJ ammo fine. Your 1:8 twist barrel will also stabilize 62 grain ammunition just fine and will stabilize projectiles of well over 70 grains as well.

As to whether you will find the .223 Remington 55 grain FMJ or the 62 grain XM855 FMJ more accurate, this will probably depend on your individual barrel and perhaps even the lot of ammo. The M855 projectile has a better ballistic coefficient than the 55 grain FMJ rounds which would theoretically give it better accuracy at longer ranges. On the other hand, the projecile core is bimetallic with a lead base and steel "penetrator" tip. If that steel core tip is not precisely uniform and precisely centered on the lead base, it can introduce wobble in the projectile's flight and degrade accuracy.

"Understabilization" of heavy (long) projectiles by barrels with too slow a twist rate is real. A 1:9 twist barrel might not adequately stabilize projectiles of greater than 70 grain mass. Whether "overstabilization" of lighter projectiles by faster twist rates degrades accuracy is debatable. I know folks with ARs with 1:7 twist barrels that shoot 55 grain FMJ ammunition more accurately than 62 grain FMJ, even when the latter has a monolithic core. A lot depends on the characteristics of the individual barrel bore and chamber, rather than the twist rate.
 
I once had a 1997 vintage Bushmaster Match Target, chambered for 5.56. 1/2 MOA with handloads.

My Colt A2 is one MOA with handloads.

I guess, for this thread, there's not a lot of difference between handloads and commercial.
 
So far, my 1:7 twist barrel shoots 55 grain 5.56 and 223 fmj better than 62 grain and 75 grain fmj. The 62 grain green tip is the least accurate out of everything I've tried, but it's close enough for plinking.

My results disappointed me a little since everything I had read told me heavier bullets would be better. The 55 grain is the easiest to find and the cheapest, so I'll get over it.
 
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