A strange trend I have noticed in my and my friend's ARs is that .223 is very consistently more accurate than 5.56. Regardless of brand, bullet weight, etc. all things being equal .223 just gives tighter groups. Anyone know why this would be?

I appreciate your input.

Diamondback 16" 1:8
PSA 16" 1:7

This is very common among all brands

The higher pressure may distort the base of the bullet.  

The 223 loads may also be tweaked for accuracy while 556 loads are loaded to meet mil-spec speeds.

The barrel and the specific load matter much more than 223/556. You can't speak of them generally as there are tons of variations that play a part.

That makes sense.

Thank you.

Absolutely I have shot 5.56 that is more accurate than some .223. However I do see a general trend.

Today for example at the range shooting at 100 yards Frontier BTHP 68 grain: the 5.56 was about 1 moa or more worse than the .223 of the same brand and bullet type. This is from 2 different platforms.

From what I've seen it depends on barrels and ammo combo. Some barrels like certain ammo. If you reload you will realize this truth.

I'm with the others that have posted................

223 might be more accurate, due to, IMHO, the idea that BC's drop if you push a bullet too hard -- too fast.
But things like chamber/twist etc play an important role too......

Can you elaborate more on this? I haven’t heard of BC’s dropping due to velocity increases, assuming you aren’t shredding jackets. The velocity difference between 223 and 5.56 isn’t going to account for enough added RPM’s to blow the bullet apart.

Certainly................
No I'm not talking about shredding jackets or blowing them up etc.
(Though I do know for a fact that if you want to blow up a bullet, use a Hornady 55 SX bullet in a 1/7" twist barrel).  

I first read of dropping BC's if a bullet is pushed too fast is from:  

"Black Magic: The Ultra Accurate AR-15" by John Feamster  1998.  Pages 157-158.
I'm paraphrasing here.............  He was talking to Dave Emary (Hornady Bullets) and testing he'd done.  Emary found that as a bullet was pushed past SAMMI pressures in a cartridge, accuracy would drop as would the BC of the bullet.  
Feamster attributed this to bullet deformation.  Then as Emary dropped the charges, accuracy returned as did the BC.  

IIRC, several articles in "Tactical Rifle" or "Accurate Rifle" magazine covered this.  But I can't find them right now.    


My personal experiences for example:  
I have shot alot of 77SMK's in various 20" AR barrels.  Of course I don't have pressure gauges nor an easy way of measuring the BC's...............
But what I've found is accuracy would shrink (get better groups) as I approached 2700-2750fps with these loads.  
Then as I worked past that, groups would get bigger and before long I would start seeing pressure signs- flattened primers etc.  
If I tried to mask the pressure signs (by say using a thicker cupped primer) and continue on, the accuracy would still get increasingly worse.

So, this is more of an over-pressure issue and not velocity?

I say that, because if I run a longer barrel, I’m going to get more velocity, but not necessarily pressure, and precision isn’t always impacted. In some cases, I can even push a bullet harder and still get great precision.


I’d definitely like to learn more on the pressure causing a drop in BC’s though. I realize that testing was done in the 90’s, so I’m curious what technology they were using, the accuracy of their measuring systems and if any additional testing has been performed.

I think he means the harder you throw it, the harder it slows down, but there's still more momentum, so I don't see BC being lower.

Most 5.56 pressure 5.56 ammos use double base ball powders that are less velocity and temperature stable. The loads with those powders are selected because they generally give higher velocity at a safe pressure and you can physically fit more powder in the case before running out of room or hitting excess pressures. These powders tend to be finicky on charge weights at high fill percentages and you get bigger deviations in accuracy and velocity as you near max charge weight based on both pressure and case volume.

Most .223 pressure match ammo is loaded with powders more conducive to accuracy than a peak velocity figure. They are loaded at a milder load that is happier in a wide variety of barrels/chambers. If the exact same ball powder is used as a 5.56 load, a charge weight is generally selected that is not up into the picky/temperamental range. If by rare chance an extruded/stick powder is used... most of those can't hit the velocity of ball powders due to casefill limits or pressure limits but are more accurate and temperature stable. Very few ball powders are temperature stable.

Basically,  the 5.56 ammo gets a charge that is on the verge of falling apart in search of a safe peak velocity and .223 gets the best accuracy charge weight with little thought to velocity.

There are always exceptions, but this is generally why .223 is more accurate than 5.56 ammo, not bullet distortion, excess RPM, or BC shifts. If those were the reasons, high 5.56 velocity loads with temperature stable extruded powders would not be able to be more accurate than .223 loads with lower charges of ball powders.

Aye.

I'm not being snarky here......... but I am choosing my words carefully as I'm sortta explaining to you what was said between Feamster and Emary...........
That said..........

Their comments:  Specifically mentioned SAMMI pressures and NOT a SPECIFIC caliber or, say, barrel length.............so yes, your comment of say using a longer barrel (with hopefully) lower pressure falls in line with their comments.  
But you would still reach a point of "pushing the bullet too hard" as you worked up, exceed the pressure and have a drop off of BC and accuracy.   That is if you accept their comments.  

Again not being snarky:  IDK the testing criteria he (Emary) did................ but that is why I fully quoted my source.  I think he is still active with Hornady. ???  Reach out to him?


If you want to further wander into the weeds about this sort of thing.................. Get and Read "The Precision Shooting Reloading Guide" Editor: Dave Brennan 1995 Precision Shooting Inc (yes same as the magazine).
In particular read Chapter 5 "Reloading for Magnums" by Jay Turner.   Around page 203............  

Again I'm paraphasing and read my words carefully............  He talks about, among other things, about a "problem with some large capacity cartridges is excessive bullet deformation while the bullet is still in the barrel.  Some shooters have reported suspected instances of jacket base 'slump" when lightly constructed bullets are fired at high velocities and pressures."  He then goes on to explain that concept further and among other things talks about how this over pressure could affect accuracy.  He then further explains that under those conditions it takes time (distance) for the bullet to settle down....... he says "go to sleep."  And the groups (accuracy) get tighter as it does.  In other words, if you push a bullet too hard, accuracy will drop........ now he comments that after some time- distance- the bullet will stabilize and you might get better groups further out.  He uses 300yds as an example.  

IMHO........ without a doubt powder selection has a large role in this too.

I appreciate the response.

It appears that the issue is really damaging the bullet and not necessarily the velocity though.

From Hornady’s website:
“Ballistic Coefficient (BC) values can, and usually do change in value with changes in velocity. Most bullets exhibit a lowering BC as velocity slows. The extent of how much a BC will change depends on each unique bullet shape.”

BC data

I know in testing 22creed loads that the ELD jackets and a 1:7- 1:7.5 twist can be a bad combo as velocity/RPM’s increase, ultimately to the point where some rounds won’t make it to the target. I would imagine that prior to this point, some rounds would have jackets that were damaged, which would impact the BC. When running Bergers at the same velocity, no deformation was noted. Hornady did confirm that the thin jackets of the ELD bullets would fail if the RPM’s were increasingly high.


I think Emary retired 5-6 years ago.

If nothing else, this has prompted me to look for additional testing that has been performed. I may load up some 77’s in the 18” AR, 26” bolt gun, 24” 22GT and see if there are some BC values that don’t align with different velocities/theoretical calculated pressures, just for my own curiosity.



As to the OP’s question, I think DevL addressed the biggest issue, typically 5.56 are pushed for velocity, with 223 being more middle of the road velocity wise in a node that works across multiple barrels. That said, IMI Razorcore, Black Hills and AAC have 77gr 5.56 loads that are still capable of sub moa precision, which is better than many can shoot consistently in an AR platform.

Another thing that harms accuracy (more correctly called precision) is bullet jacket non-uniformity. When a jacket is non-uniform and out of balance, it is a proven fact that faster twist rates will degrade accuracy slightly. The faster the twist, the greater the dispersion. This is due to more wobble effect from more RPMs over a particular distance. If you have a higher launch velocity with a fixed twist, this also increases bullet RPM. And while velocity decreases over distance, RPMs stay essentially the same for the entirety of a bullet's flight path. In this case, higher velocity will always result in increased dispersion, just to a lesser extent than a faster twist.

The way around that is to shoot bullets with near perfect jacket uniformity, AKA match bullets. If there is no jacket non-uniformity there is nothing to amplify.  Kind of like how even if your parallax is off but you have your eye perfectly centered in the optic, you have zero parallax shift/error. With bullets that have poor jacket uniformity, AKA mass produced military FMJ bullets, there is a negative correlation to accuracy from both twist rate and to a lesser extent, velocity.

But oddly, out of the IMI Razorcore 77gr 5.56 BTHP and Black Hills and AAC 77gr 5.56 TMK and SMK loads, the fastest is the Black Hills, yet it is also the most accurate across most rifles. And there are IMI and AAC loads using the same 77 grain Sierra Match King bullet that Black Hills uses... yet Black Hills is still the most accurate of the three, generally.

In fact, I know of no other .223 or 5.56 factory loads that are MORE accurate than the Black Hills 77gr loads across multiple rifles, provided they have a twist fast enough to stabilize them. Occasionally, a rifle will love some particular factory .223 loading, like a 69 or 77 Federal Gold Medal Match, or a Hornady 55gr VMAX, etc. but across the board, the Black Hills 77 grain loadings are like unicorns in about 80% of 223/5.56 rifles. In the remaining 20% of rifles, they are just sub 2 MOA loads that never shoot MOA or less. Why? I have no idea.

Fair enough and in looking at my original post............ I was being brief and didn't want to write a book that noone would read...........
There are far more immediate factors to the question of accuracy than this....... "over pressure"/"bullet deformation etc" whatever road this thread veered down.  
And you are bringing one up................ if the bullet jacket in question is not uniform, it will wobble down the bore, down range and you will see that on paper.  No doubt.  Or to be more precise and echo your comments........ the less uniform the jacket is, the less accuracy you will see.  
And alot of "5.56 Ball" is loaded with mass produced bullets with far looser uniformity............ so accuracy suffers.  

Yes, BHA offers VERY consistant and accurate ammunition.

I think there may have been some confusion stemming from the initial discussion. Perhaps I misunderstood the message being conveyed, as I took it as you saying that pushing bullets faster would result in a decreased BC, I.e, the increase in velocity from 223 to 5.56 could damage the bullet. Instead, it appears we may be saying the same thing; if a bullet is damaged, as a result of numerous variables, the BC and potentially the precision would be impacted.

I’m aware that pressure builds and yields velocity. But changing of powders or barrel length can result in increased velocity but not necessarily increasing pressure beyond a cartridge’s pressure “max” for a given bullet.

I agree, BH’s 77 grain loads are typically the fastest of what is currently available. The IMI and AAC loads have been comparable for me, with the newer IMI and AAC being closer in velocity (seems IMI is running closer to 2750fps in the newer lots I have). I have no desire to argue; I have no axe to grind. I realize it may have no bearing on this discussion, but I wanted to try and clear the proverbial air. I didn’t understand your implication of a “snarky” reply earlier, but it appears you may have some immediate disdain towards my posts due to a continued incorrect perception that I’m sponsored by a company that you clearly don’t like. As I stated in your CBC vs AAC thread, I wasn’t in the past and at the time of this post, I am not a sponsored AAC shooter.

Firstly I apologize for sidetracking this thread and veering off into a some what minute detail in this thing we call accuracy.

But I'm thrown off by the apparent skepticism shown towards the concept I'm presenting here.
Maybe I'm not explaining it well enough or maybe it's just me.  
But I assumed this was well known and accepted.  

I'll explain it differently:
Every Reloader has a process for developing a load for their firearms.  
Some simply copy one another but alot go thru a process and they all follow the same basic principle.  

You take a particular bullet/powder charge and start "working up".......increasing the powder charge.... which all things being equal increases the pressure/velocity.  
Some then look simply at group size, some use a "ladder approach" and look for groups that overlay one another or, say, when SD shrink notably to see which is best.
Now, of course, you wont know that until you go past that, that is to say ........you'll end up with some groups before and after the "sweet spot" you are looking for.  
Some simply believe you keep going until you see excessive pressure and "back off" a certain amount under the belief that that is where accuracy lies....... just before "excessive pressure signs."

So what all these do, in different ways, is increase the charge (or pressure, which we measure in velocity) looking for a "sweet spot" where the combination of the components works best- is the most accurate.
There maybe multiple "sweet spots" but as you work up and unknowingly past the last one......... accuracy will drop off again.  
And at some point, if you keep going, you reach the limits of that combination of components........ you cant stuff any more powder in or the primers fail, the primer pocket opens up etc etc.
So you are stopped by excessive pressure and the fact that better groups are found before that.
Any of you that have done load testing will have seen this result............ so why is so foreign to you?

Or in other words............ at some point, be it a 22lr, 223, 308, 50Cal ............excessive pressure (which we measure in velocity) will cause a drop off in accuracy.  
Now Feamster and Emary were saying anything past SAMMI spec pressures is excessive and more you go past that........ then of course accuracy will suffer and the BC will drop.
   

My "snarky" comment was about when I suggested that instead of having me try to explain Emary's comments/testing that instead you try to talk to him directly about it.  And I didn't want to leave you with the impression that I was, in effect, telling you to ### off.  
So I was actually trying to show you some respect and not sidetrack this conversation.
As far as whatever your or my relationship to AAC is or isn't is for another thread............... that's REALLY off topic here.  Just like whatever you and I do or dont think of one another.  
But you're mistaken on at least one thing..............  one of them being that I don't like AAC......... I posted open and honest tests of their ammo.  I posted what I found........ good and bad.   And there are alot of "goods" in their ammo.  There are some bads.....and if AAC management is reading these threads, like they sometimes do, maybe they will make some changes that benefit us all.

Pmax can be reached with Red Dot, Blue Dot, H4198, IMR3031, Benchmark, and CFE223, with respectively rising muzzle velocity.

ETA: The back of my memory says there were some short-fat cartridge loads that suffered from some magnum primers slamming the bullet into the lands. Perhaps the barrels were excessively freebored and with too steep a leade. Doesn't seem to affect 5.56, but food for thought.

Anything over SAAMI certainly is not a realistic definition of the accuracy limit. Pretty much anyone who loads 6.5 Creedmoor finds their accuracy node above the SAAMI max pressure.

Also, there are plenty of cartridges that use the same bullets as smaller capacity cartridges and deliver excellent accuracy at higher velocity. If the velocity was the issue, the larger capacity cartridges could never shoot lighter bullets well.

For example, you shoot 6.5 Creedmoor and find with a particular bullet anything above 2750 fps results in a decrease in accuracy. You load the same bullet pushed to higher velocity in 6.5 PRC and easily push way past 2750 fps with great accuracy. Just velocity harming the projectile can not be a factor in why the 6.5 Creedmoor could not be pushed past 2750 fps.

It is a well established fact certain projectiles are harmed by velocities over a certain level. The tips of AMAX bullets melting that led to the ELD polymertips by Hornady is a perfect example. But this is not why 5.56 is generally less accurate than .223 across the board.

Consider a triad of things when it comes to bullets, chambers-throats, and velocity.

Some bullets with thinner (i.e., J4) target jackets deform or engrave differently.

Throat leades with shorter free-bore jump (i.e., bullet ogives just kissing the leade-land "Ramp") tend to align magazine-length rounds coaxially to the bore as opposed to having to take a free-running start before skid-engraving into rifling.  A bullet with more run-out risks being spun with a point wobbling off-axis, perhaps just a miniscule bit.  Gas blow-by will also be more in a longer free-bore (5.56 mil-standard) than one cut with a shorter-throated Compass Lake reamer.

Chamber pressure and the curve affects how quickly the bullet clears the case mouth, skid-hits the leade, starts into the rifling, and spinning.

Thicker-jacketed Sierra Match Kings tend to be more jump-tolerant than others.

Highpower M16/AR shooters have to compromise somewhere when it comes to their shooting discipline.  A shorter throat favors magazine-length bullets but requires a shorter ejection port single-fed round with longer bullets (75 very low drag, A-Maxes, and 80-grain Sierras, etc.) for 600 yards.  A longer throat (allowing for more powder) means you have to have a slight free-bore "Jump" with your magazine-length short-line (200 and 300-yard) ammo (69s, 73s, 75s, and 77s).