What is the limiting factor in ball 5.56 Nato Ammo?

What I read on the internet matches how I shoot. 5.56 Nato Ball Ammo generally gives 4 to 5 inch groups at 100 yards.

My question is: What is the limiting factor?

a) the bullet is unstable over the last 75 yards

b) the bullet does not leave the barrel in a uniform fashion

c) the cartridges are loaded to low tolerances, giving inconsistent residence time in the barrel.

Thank you in advance

That is not good at only 100 yards.

What bullet weight are you shoiting? What is the twist rate? Your barrel might not be capable of stabilizing the bullet you're shooting.

Even the poorest quality bulk should be capable of better than 4 or 5 inches at 100 yards.

55gn military surplus will shoot better than an inch at 100yds and will hold 6-8" at 500yds if you hold 'em and squeez 'em.

I get 1 inch groups with factory loaded Sierra Match King BTHP and 4 inch groups with American Eagle 5.56

Let me guess. Your barrel twist rate is 1/7. Your chamber is 5.56 NATO. You're shooting 55-62 grain ammo.

We need more information.

Heck I'll bet most of those groups are shot with the M-4 carbines. Even the crappy steel cased Russian stuff shoots well under 2 inches out of my Bushmaster Varminter. I don't shoot that stuff very often. I just found a few boxes down in the vault.

+1 with matching the bullet weight to the barrel twist.

even though my 1:14 will shoot a 70gr speer RN and get .55" at 100 yards
it opens up to 3.5" at 200 yards.

A 52gr BT/HP will get 1" at 200 yards.

Your chamber spec's will also come into play.

The accuracy you are getting is consistent with the accuracy standards required by the US government for M855 ball:

MIL-C-63989C 3.11 Accuracy. Both average vertical standard deviation and the average horizontal deviation shall be no greater than 6.8 inches at 600 yards, or alternatively, no greater than 1.8 inches at 200 yards using an indoor range.


The components are manufactured and loaded to the degree of consistency appropriate for assault rifle and light machine gun use instead of match use.

bushmaster1313 said:

What I read on the internet matches how I shoot. 5.56 Nato Ball Ammo generally gives 4 to 5 inch groups at 100 yards.

My question is: What is the limiting factor?

a) the bullet is unstable over the last 75 yards

b) the bullet does not leave the barrel in a uniform fashion

c) the cartridges are loaded to low tolerances, giving inconsistent residence time in the barrel.

Thank you in advance

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Well, since you read on the internet it must be true, right?
A) Stability beyond 75 yards is not the issue.
B) I could see that with a sloppy bore, bad muzzle crown, or a real skinny, whippy barrel, especially as it gets hot.
C) Most ammo is uniform, but that's not to say that some really cheap ammo is not going to have issues.


Most 5.56x45 ammo will hold 2 inches or less at 100 yards, but the bullet weight needs to be compatible with the barrel's rifling twist and the barrel must be of good quality and not prone to warping as it heats. Of course, you also need a firearm with a good trigger and good optics in order to get those 2 MOA or smaller groups.

V0OBWxZS16 said:

The accuracy you are getting is consistent with the accuracy standards required by the US government for M855 ball:

MIL-C-63989C 3.11 Accuracy. Both average vertical standard deviation and the average horizontal deviation shall be no greater than 6.8 inches at 600 yards, or alternatively, no greater than 1.8 inches at 200 yards using an indoor range.


The components are manufactured and loaded to the degree of consistency appropriate for assault rifle and light machine gun use instead of match use.

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Your reply makes no sense. The accuracy the OP is getting - 4-5" @ 100yds - is more than 4x the accuracy standard of the spec you cited.


The OP's accuracy issue is most likely not ammo quality related. As mentioned above, it could be twist related or any of a couple dozen other mechanical and technique issues.

V0OBWxZS16 said:

The accuracy you are getting is consistent with the accuracy standards required by the US government for M855 ball:

MIL-C-63989C 3.11 Accuracy. Both average vertical standard deviation and the average horizontal deviation shall be no greater than 6.8 inches at 600 yards, or alternatively, no greater than 1.8 inches at 200 yards using an indoor range.


The components are manufactured and loaded to the degree of consistency appropriate for assault rifle and light machine gun use instead of match use.

Click to expand...

I could (and still can) rely on about 1.5" five shot groups at 100 yards with M193 (55 gr FMJBT) in an M16A1 or an early AR-15. You won't get that with M855 (62 gr FMJBT) due primarily to the less consistent nature of the penetrator equipped SS109 projectile and lower ammunition quality and acceptance criteria over all.

The fact that M855 is over stabilized in a 1-7 twist barrel (1-9 is optimum for a bullet of that length, 1-7 was adopted to accommodate the much longer M856 tracer round) doesn't help accuracy either. Excessive spin results in greater yaw and precession with a lower quality bullet. As the bullet exits the bore it has to transition from spinning around the center of form to spinning around the center of gravity. That produces yaw, and the excess spin increases the precession that occurs, and aerodynamic forces acting on the bullet cause it to take a spiral flight path.

That spiral flight path eventually dampens out after a couple hundred yards, but with successive bullets on slightly different trajectories. That's great for a machine gun where a cone of fire is more useful than precise accuracy, but it's not great if you are engaging point targets with single shots.

The fact is the SS109 projectile and the subsequent M855 ammo were designed for use in a machine gun and the M16A2 and M4 were designed to be compatible with the M855 and M856 rounds. The tradeoff is poor accuracy compared to M193 in the M16A1.

Let us also remember that the.556 was a round made for WAR and no ttarget shooting. The idea is to hit the bad guy/enemy/terrorist, I do not thing that Stoner when developing this round intended it ot be a MOA target round.
One other thought occurred to me...could the limiting factor here he the shooter??? Is this 4" grouping offhand? Open sights?
Me, if I could shoot 4" groups with open sights standing at the range, I'd be pretty happy with that. But then again I'm easy to please

The MilSpec requirements quoted are referring to the " deviation" , ie the radius from the group center, not the group size . For a 1.8in deviation, that would equate to a 3.6in Diameter group .

What specific NATO ammo are we discussing ? M193 ? M855 (SS109) ? Mk 262 & variants ? The various " Green" ammo ?

What rifle, what chamber ?

Could y'all imagine knocking down that 300 yard green Ivan with open sights and a 5" MOA? Yikes.

WNC Seabee said:

Your reply makes no sense. The accuracy the OP is getting - 4-5" @ 100yds - is more than 4x the accuracy standard of the spec you cited.

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Standard deviation is not the same thing as group size. Standard deviation is is sort of like an average of how away the shots are from the center of the group. Assuming a normal distribution having a standard deviation of 1.8 inches at 200 yards means about 33% of the shots will be outside that limit. So groups will be larger than standard deviation.

But I agree that 4 to 5 inch groups at 100 yards is not normal or acceptable.

My AR has a 5.56 chamber, 1 in 7 twist and does much better than that. But I do get larger groups with Winchester 55 grain FMJ and Federal XM193 than I do with .223 ammo loaded with light ballistic tip style bullets.

When I first got my AR I put a ridiculously large scope on it to see what it could do. The best groups I got were with Fiocchi and Black Hills .223 loaded with Hornady 50 grain V-max bullets, both of which produced 5 shot groups under .75 inches at 100 yards despite the 1/7 twist and NATO chamber. The ammo with heavy bullets I expected to be most accurate did well but could not match the results with the light bullet ammo. But with 55 grain FMJ ammo the groups varied from about 1.25 to a little over 2 inches.

I am not sure why the military style ammo does not group as well but suspect it is because the bullets have thicker jackets, a less pointed tip instead of a match style HP or ballistic tip and are not as consistent. Since I took the large scope off and started using iron sights or a red dot my 60 year old eyes are not going to be shooting .6 inch groups with any ammo. The military ammo is accurate enough for its purpose and using a FMJ design is rugged, more reliable and less expensive.

bushmaster1313 said:

What I read on the internet matches how I shoot. 5.56 Nato Ball Ammo generally gives 4 to 5 inch groups at 100 yards.

My question is: What is the limiting factor?

a) the bullet is unstable over the last 75 yards

b) the bullet does not leave the barrel in a uniform fashion

c) the cartridges are loaded to low tolerances, giving inconsistent residence time in the barrel.

Thank you in advance

Click to expand...

Hard to understand exactly what you are asking. Most who shoot cheap bulk ammo (if that's what you are referring to) with 55-62 grain bullets don't have a primary interest in fine accuracy, but such ammo is generally capable of 2 1/2" - 3" groups at 100 yards, assuming gun and bore are in decent shape.

THEmodelof1989 said:

Could y'all imagine knocking down that 300 yard green Ivan with open sights and a 5" MOA? Yikes.

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And yet, we all did, right?

Could you even qualify, if you missed all the 300 meter shots?

My AR-15 is Windham M-16A4 style factory gun, rip roaring ready to go for service competition, fit with a 1:7 twist for big match bullets. I know its not the right pairing, but I've mostly fed it 55 grain NATO ball because its brass and its cheap at the local WalledMart. Good enough for off hand rapid fire, and even when I've informally shot some paper from prone it seems like it can do 3 inches at 100 yards, perhaps better if I tried harder or put optics on it with sandbags and a good rest. 4 inches at 100, or worse, indicates an issue with the shooter and/or the rifle in question.

From what I've read elsewhere, others with the 1:7 have had a similar experience, not the worst groups at 100 yards and not seeing the worst of the barrel twist dilemma till a little further out. So, no insult or disrespect intended, but often times the limiting factor in a combat rifle especially is the shooter. Its possible to get the tightest groups possible out of them, but its also easy enough to add a little width to that group with a factory trigger and iron sights.

Steve912 said:

And yet, we all did, right?

Could you even qualify, if you missed all the 300 meter shots?

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You could qualify, but you'd never hit expert.