.223 &/or 5.56mm Bushmaster


August 23, 2007, 02:50 AM
I have a Bushmaster E2S with the 20" barrel. It's marked on the receiver .223-5.56mm. Does this mean that I can use either load - .223 &/or the 5.56? I know the differences between the .223 & 5.56. I've been shooting .223 ammo from it so far & the Hornady 55 grn moly factory load does quite well but some of my handloads don't fare so well. I'm not shooting hot loads in it. A typical load is 25 grns of AA2230 under a 55 or 50 grn Hornady V-Max bullet. But from what I've read & understand, if it's a 5.56, the rifle would shoot better groups with actual 5.56 ammo or at least with loads duplicatiing 5.56mm.

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August 23, 2007, 03:03 AM
From wikipedia

"While the 5.56 mm and .223 cartridges are very similar, they are not identical. Military cases are made from thicker brass than commercial cases, which reduces the powder capacity (an important consideration for handloaders), and the NATO specification allows a higher chamber pressure. Test barrels made for 5.56 mm NATO measure chamber pressure at a the case mouth, as opposed to the SAAMI location. This difference accounts for upwards of 20,000+ psi difference in pressure measurements. That means that advertised pressure of 58,000 psi for 5.56 mm NATO, is around 78,000 psi tested in .223 Rem test barrels. The 5.56 mm chambering, known as a NATO or mil-spec chambers, have a longer leade, which is the distance between the mouth of the cartridge and the point at which the rifling engages the bullet. The .223 chambering, known as SAAMI chamber, is allowed to have a shorter leade, and is only required to be proof tested to the lower SAAMI chamber pressure. To address these issues, various proprietary chambers exist, such as the Wylde chamber (Rock River Arms)[1] or the Armalite chamber, which are designed to handle both 5.56 mm and .223 equally well.

Using commercial .223 cartridges in a 5.56-chambered rifle should work reliably, but generally will not be as accurate as when fired from a .223-chambered gun due to the excessive lead.[2] Using 5.56 mil-spec cartridges (such as the M855) in a .223-chambered rifle can lead to excessive wear and stress on the rifle and even be unsafe, and the SAAMI recommends against the practice.[3] Some commercial rifles marked as ".223 Remington" are in fact suited for 5.56 mm, such as many commercial AR-15 variants and the Ruger Mini-14, but the manufacturer should always be consulted to verify that this is acceptable before attempting it, and signs of excessive pressure (such as flattening or gas staining of the primers) should be looked for in the initial testing with 5.56 mm ammunition.[4]"

This question has been answered here at least twice since I've been here, and at least 100 times before I'm sure ;)

August 23, 2007, 03:22 AM

Bwana John
August 23, 2007, 10:43 AM
The lower receiver has NOTHING to do with the dimentions of the chamber in the barrel.:banghead:

The lower receiver could be marked 9mm, 6.8, 223/5.56, 45 SOCOM, .577 Tyrantosoris Rex or whatever...:neener:

This 223 vs 5.56, and 308 vs 7.62 stuff has gotten a little out of hand.:cuss:

August 23, 2007, 11:42 AM
My post has nothing to do with the differences between .223 & 5.56. That was not my question.

I stated that the receiver on my AR was marked .223-5.56mm. I also stated that I KNOW the difference between .223 & 5.56mm. Also, if the lower receiver were marked 9mm, 6.8, or .557 T-Rex, I think I'd be concerned about running .223 ammo thru it without confirming what caliber the d*mn thing was. I know it's a big stretch, but usually when a mfg marks a rifle .223 or 30-06, or laser beam quantum blinder, then it's probably chambered in that.

My question was - since my receiver is marked as stated, .223-5.56mm, & that is the only markings on the receiver identifying caliber, does that make it safe/preferable to shoot 5.56mm ammo from this rifle? This is not a kit gun. It was purchased as an entire unit from Bushmaster.

Again - I'm trying to address the preferences of the rifle, NOT the differences between .223 & 5.56mm.

August 23, 2007, 12:06 PM
Alright - I found Bushmaster's customer service phone number. It turns out that all Bushmasters are roll stamped on the barrel just in front of the gas block with the caliber designation. Mine is stamped 5.56 NATO. Bushmaster makes 3 rifles that are .223 only & sorry, but our phone connection wasn't that good & I couldn't make out the 3 models the guy told me.

August 23, 2007, 12:20 PM
know it's a big stretch, but usually when a mfg marks a rifle .223 or 30-06, or laser beam quantum blinder, then it's probably chambered in that.

The reason that the poster said that it doesn’t matter what the lower receiver is stamped is because the lower of an AR has little to do with the chambering, per se, due to the AR being modular. For instance I have my 6.5 Grendel upper on a DPMS low that is marked 5.56/.223.

August 23, 2007, 12:33 PM
DogBonz -
I understand that per the receiver markings, but like I said earlier, that wasn't my question. At the time I posted the question, I didn't know (or notice) that Bushmaster stamped their barrels just in front of the gas blocks. My total experience with rifles has all been with bolt actions. I know their barrels are labeled for the cartridge they're chambered for, but then, per say, they don't have a "receiver" to be marked either.

The one thing I totally wanted to avoid was the .223 vs 5.56 thing. And that's all I got. Guess I was a bit frustrated in the replies since I did state in the first posting that I knew the difference between .223/5.56 & that I didn't want to get into that discussion.

Thanks anyways DogBonz.

August 23, 2007, 12:35 PM
I don't think your rifle will "prefer" one over the other but I do know that you can put together more accurate loads than military surplus.

If it means anything, I run NATO pressures with military brass through my RRA and lower pressure loads through commercial brass and I haven't noticed huge differences. I haven't really tested the Bushmaster I replaced it with to its real potential yet. The RRA was a Wylde and this Bushmaster is a NATO.

August 23, 2007, 12:40 PM
Double post.:confused:

August 23, 2007, 12:48 PM
Agree with what gipper said, although on some Bushmasters the indicator on the barrel is under the handguard. If you don't find a marking on the barrel, you may not have a 100% Bushmaster rifle.

August 23, 2007, 01:48 PM
Yeah, don't worry about what the receiver says on an AR, worry about what the barrel says.

Bwana John
August 23, 2007, 01:49 PM
My total experience with rifles has all been with bolt actions. I know their barrels are labeled for the cartridge they're chambered for, but then, per say, they don't have a "receiver" to be marked either.
The "receiver" on a bolt action is that thing that the bolt goes back and forth in.
Usually they are marked for manufacture and not caliber, as they can be used for many different caliber. (just like an AR lower)

August 23, 2007, 02:00 PM
A 5.56 leade is longer than .223 They tend to shoot bullets with a shorter ogive better (not as "pointy") this usually means lower BC bullets, they will fit in the mag, but the bullet contacts the rifling sooner. an A-max bullet has a fairly long ogive, and shoot great in .223 barrels, but not as well in 5.56, I have had good luck with HDY 55gr FMJ in my AR, and even have done well with soft point varmint bullets, but at longer ranges (more than 300yds) SMK are the most consistent, and get better, the further out you are shooting.

August 23, 2007, 02:20 PM
There is a good article in the most recent issue of American Rifleman about .223 vs. 5.56 in AR's. Last, or second to last, paragraph of the article tells you you can put one, but not the other, in an AR. Sorry, I do not remember how it goes. HTH, FWIW.

August 23, 2007, 02:24 PM
All Bushmaster barrels are cambered for 5.56 NATO except for their non-chrome lined match and varmint barrels. Those have a hybrid chamber, probably similar to the WYLDE chambering, that still allow 5.56 NATO to be used while offering better accuracy like the SAMMI .223 spec.

August 23, 2007, 02:28 PM
gipperdog, head over to the reloading forum and do some searching for AR-15 specific loads and processes. The reloading section at arfcom is good for this too.

August 23, 2007, 02:59 PM
Bwana John -

That's the kind of smart ass replies I was talking about earlier. :cuss:
I never said or implied that bolt action rifles don't have a receiver nor that I didn't know what one was. :fire:
I said that they are NOT marked, typically, for cartridge or caliber on a bolt gun.
I've been shooting for 43 years, since I was 7 yrs old. I know what a freaking receiver is. :mad:
I only implied that I've not had a lot of experience with rifles like the AR except for the one I own now & my 4 years in the Army - 25th Inf Div.
I have right now, 8 bolt action rifles from - 2 ea. 22LR, a 7mm Rem Mag, a 300 Win Mag, a 6.5x55 M96, a 308, a 22-250, & a .338 Win Mag.

August 23, 2007, 04:46 PM
.223 Remington vs. 5.56: What’s In a Name

By BRYCE M. TOWSLEY field editor
American Rifleman – September 2007

Most gun guys know the history of the .223 Remington and that it - like so many of our popular cartridges - started life in the military. Because the military switched to metric designations sometime in the 1950s, this little .22-cal. cartridge was later called the 5.56x45 mm NATO (commonly referred to as "5.56x45 mm").

The 5.56x45 mm surfaced in 1957 as an experimental cartridge in the AR-15 rifle. The concept was to develop a smaller, lighter military cartridge that would still be traveling faster than the speed of sound at 500 yds., and this was accomplished by using a 55-gr. boattail bullet. The AR-15 evolved into the select-fire M16 rifle that was adopted by the military in 1964.

Even though it would ultimately kill off its own .222 Rem. and .222 Rem. Mag. cartridges, Remington was quick to act, and very shortly after the military adopted the 5.56x45 mm cartridge the firm brought out the civilian version, called the .223 Remington. Confusion followed.

The common misconception is that the two are the same; that 5.56x45 nun and .223 Rem. are the same dance partner, but with a different dress. This can lead to a dangerous situation. The outside case dimensions are the same, but there are enough other differences that the two are not completely interchangeable.

One big difference is pressure. It becomes a bit confusing, as the pressure for the two is not measured in the same way. The .223 Rem. is measured with either Copper Units of Pressure (c.u.p.) or-more recently-with a mid*case transducer in pounds-per*square-inch (p.s.i.). The military 5.56x45 mm cartridge is measured with a case mouth transducer. The different measuring methods prevent a direct comparison, as a case mouth transducer gives lower numbers on identical ammuni*tion when compared to those from a midcase transducer. That's because the pressure is measured later in the event, after the pres*sure has already peaked. Accord*ing to Jeff Hoffman, the owner of Black Hills Ammunition, military ammunition can be expected to hit 60,000 p.s.i., if measured on a Sporting Arms and Ammunition Manufacturers' Institute (SAAMI) mid-case system. Black Hills loads maximum average pressure is 55,000 p.s.i., while a 5.56x45 mm measured with a case mouth trans*ducer has a maximum average pressure of 58,700 p.s.i.

While the 5.56x45 mm chamber is slightly larger than the .223 Rem. chamber in just about every dimension, the primary difference is throat length, which can have a dramatic effect on pressure. The 5.56x45 mm has a longer throat in the chamber than the .223 Rem. The throat is also commonly called the leade, which is defined as a portion of the barrel directly in front of the chamber where the rifling has been conically removed to allow room for the seated bullet. Leade in a .223 Rem. chamber is usually 0.085", while in a 5.56x45 mm chamber the leade is typically 0.162", or almost twice as much as in the .223 Rem. chamber. Also, the throat angle is different between the two chambers, and that can affect pressure rise and peak pressure.

SAAMI regulates cartridge overall length, but not bullet ogive design. The shape of the ogive can significantly affect how far the bullet jumps before contacting the rifling. Some 5.56 mm bullets have an ogive suitable for 5.56 chambers with the longer throat, but if they were cham*bered in a .223 Rem., it could result in very little, if any, "jump" to the rifling. This can increase pressures. Remember, the 5.56x45 mm already starts out at a higher pressure. If the higher-pressure 5.56x45 mm cartridge is then loaded into a .223 Rem. firearm with a short throat, the combination of the two factors can raise chamber pressures.

If you are a handloader, you must also consider that the 5.56x45 mm cartridge case may have a thicker sidewall and a thicker head, which were designed to withstand the stresses generated by the higher chamber pressures. This reduces the powder capacity of the case. If the 5.56x45 nun case is reloaded with powder charges that have proven safe in .223 Rem. cases, this reduced internal capacity can result in much higher chamber pressures.

Bottom line? It is safe to fire .223 Rem. cartridges in any safe gun chambered for 5.56x45mm. But, it is not recommended and it is not safe to fire 5.56x45 nun cartridges in a firearm chambered for .223 Rem.

In fact, the 5.56x45 mm military cartridge fired in a .223 Rem. chamber is considered by SAAMI to be an unsafe ammunition combi*nation and is listed in the "Unsafe
Arms and Ammunition Combinations" section of the SAAMI Technical Correspondent's Handbook. It states: "In firearms chambered for .223 Rem. - do not use 5.56x45 mm Military cartridges."

There is no guarantee, however, that .223 Rem. ammunition will work in 5.56x45 mm rifles. Semi*automatic rifles chambered for 5.56x45 mm may not function with .223 Rem. ammunition because they are designed to cycle reliably with the higher pressure and heavier bullets of the 5.56x45 mm particularly with short barrels. While problems are rare, they do not indicate that the ammunition or rifle are defective. Like some marriages, they are simply incompatible.

When shooting .223 Rem. cartridges in a firearm chambered for 5.56x45 mm, it's likely that there will be a degradation in accuracy and muzzle velocity due to the more generous chamber dimensions. That's not to say that a firearm chambered in 5.56x45 mm won't be accurate with .223 Rem. loads, only that, on average, the .223 Rem. chambered firearms will be more accurate with .223 Rem. ammunition than rifles chambered for 5.56x45 mm firing .223 Rem.

Another issue is the twist rate of the rifling. The SAAMI specification for .223 Rem. is a 1:12" twist, and most non-AR-15-type rifles will use that rate. But, this is a cartridge that crosses a wide spectrum of uses, and as a result there is often a wide deviation from the 1:12" twist rate, particularly in the very popular AR-15-style "black guns." There are bullets available for the .223 Rem. that range in weight at least from 35 grs. to 90 grs. With that wide of a spectrum, one twist rate is not going to be enough.

Firearms chambered for 5.56x45 mm often have a rifling twist rate of 1:7" to stabilize the long, sleek, heavy bullets used in long-range shooting. Any rifle with a 1:7" twist rate will work best with bullets heavier than 60 grs.

On the other hand, a 1: 12 twist rate (most bolt-action .223 rifles) will stabilize most bullets up to 60 grs., however some longer 60-gr. bullets will not shoot well with that twist rate. Many firearms use a 1:9" twist, which is a very good compromise that works well with most bullets up to 70 or 75 grs. The great thing is that if you have a good barrel and quality bullets, the 1:9 works well with even the lightest bullets.
What does all this mean? If you have anAR-15 type firearm with a 5.56x45 mm chamber you can shoot either .223 Rem. or 5.56x45 mm safely. If your twist rate is 1:7" you should use bullets weighing 60 grs. or heavier. If you have any rifle with a 1:12 twist you should shoot bullets of 60 grs. or less for best accuracy. If you have a .223 Rem. rifle of any type, it is not recommended that you use 5.56x45 mm ammunition.

August 23, 2007, 11:31 PM
What W.E.G. said.
We have had folks buy 5.56 NATO military surplus at the shop and then bring it back because they couldn't get it to chamber in their Remington/Savage/Winchester bolt action .223, or if it did chamber it was all but impossible to get the bolt open and the fired case extracted.

An AR type rifle chambered in 5.56 NATO will generally shoot .223 Remington cartridges fine.
Some commercial .223 Remington cartridges have cases that are a little on the soft side and they sometimes fail to extract in some 5.56 NATO chambered rifles but this is a trial and find out issue more that a problem.

(And everybody thinks only steel cases cause problems in AR rifles :eek:)

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