Why have both .223 and 5.56?

[W.E.G.]

 

[wally]

Many commercial guns have throats open enough to safely shoot 5.56, so just because example X of whatever model shoots tons of them and its marked 223 doesn't by any means mean any gun marked 223 is also safe to do so, its individual with the way the maker chose to ream the throat. Ruger has always stated that their 223 guns were safe to fire 5.56 ammo in.

This comes up all the time. I'm still waiting for a documented example of a .223 gun damaged by firing factory 5.56 ammo or vice-versa.

"Optimal" accuracy is a separate issue and is not safety related, but darn near any gun will have an accuracy preference for some ammo compared to others.

 

[Arizona_Mike]

Short answer: .223 SAAMI has been set in stone since 1964. The military is not bound by SAAMI and has changed the throat for longer heavier bullets.

Mike

 

[Malamute]

I think drawing a line between .223 Remington and 5.56x45mm came when bullets heavier than 55 grains came into common use with the military loadings, requiring different bullet throats and rates of twist for barrels using 62gr bullets and heavier.

Do you have any further information about this? I hadn't heard there was any difference in throats when the rifling twist rate was changed for the newer heavier bullets.

This comes up all the time. I'm still waiting for a documented example of a .223 gun damaged by firing factory 5.56 ammo or vice-versa.

I haven't heard of it causing damage either, but have heard of blown primers being fairly common in some ARs chambered in 223 (despite being marked 5.56). They stopped showing pressure issues when a 5.56 chamber/throating reamer was used on them with the same ammo. This was noted in carbine classes, the instructor had seen enough of these sort of problems and bought the reamer to clean them up on the spot at the classes.

In the link I posted earlier, it was noted that one individual pressure tested 5.56 ammo fired in a commercial 223 chamber and was getting rather high pressures,

I fired XM193 5.56 ammunition in a 223 test barrel with average pressures (conformal transducer) of 72,550 psi, and peak pressure registered at 76,250 psi. . ."

So, no, it didn't break the gun, but it is going to put more stress on the case, and potentially have pierced primers which can damage the firing pin. Id choose not to shoot ammo that was potentially that much higher than standard, if others choose to, OK by me. The bottom line seems to be that there isn't any guarantee that any individual rifle will have problems, or is going to blow up in anyones face, but the variables in actual chambering by various manufacturers leaves the possibility that it may be running higher than desirable pressures to shoot 5.56spec ammo in a 223 commercial chamber. I suspect that it may be more common to give a little longer throat to commercial 223 chambers than in the past, but one never knows for certain what their individual gun has unless they do a chamber/throat casting and checks it. Its a bit bothersome that some AR barrels are marked 5.56 but don't seem to actually be so chambered/throated.

 

[denton]

The maximum COL for M855 and M193 is 2.26", per the drawing.

The SAAMI maximum COL is 2.260".

The same.

I believe that you are correct. I temporarily cross-combobulated cartridge length with chamber length.

The whole EPVAT/SAAMI pressure spec thing is a bucket of worms. Measuring pressure at the middle of the cartridge with a perforated case gives one result, measuring with a non-perforated case gives another, and measuring at the case mouth gives a third. As nearly as I can determine, you cannot simply dial in the offset from the pressure containment of non-perforated brass and get the case mouth figure. The difference between perforated an non-perforated mid-case measurements tends to be about 5,000-7,000 PSI because the brass bears some of the gas containment load.

The military spec for M193 is 3,250 FPS from a 20" barrel. The SAAMI spec for 55 grain 223 Rem is 3050/3215 FPS from a 24" barrel. So it must needs be that military 5.56x45 is loaded hotter than SAAMI specs.

 

[Bart B.]

In the USA, pressures between the .223 and 5.56 rounds is insignificant. Commercial ammo’s based on the SAAMI pressure standards and military ammo uses the SCATP system based on the SAAMI commercial one. .223 average pressure’s 55,000 psi for USA’s SAAMI commercial specs, the 5.56 NATO pressure’s 55,114 psi average for USA SCATP military specs.

 

[denton]

.223 average pressure’s 55,000 psi for USA’s SAAMI commercial specs, the 5.56 NATO pressure’s 55,114 psi average for USA SCATP military specs.

How, then, does M193 get more speed out of a 20" barrel than the SAAMI spec for 223 out of a 24" barrel? I can't reconcile your statement with that fact.

Also, the Accurate/Western book lists a 223 load for the 55 grain Hornady BT-FMJ of 25.8 grains of TAC for 3293 FPS out of a 24" barrel, 2.200" COL. A bit down the page, they list a 5.56x45 load, same bullet, same barrel length, same COL, but 27.3 grains for 3450 FPS.

Disentangling different measurement systems is messy in this case. Whatever conclusion we reach has to be consistent with these facts.

 

[Malamute]

How, then, does M193 get more speed out of a 20" barrel than the SAAMI spec for 223 out of a 24" barrel? I can't reconcile your statement with that fact.

The throating of the barrel. The part many seem to be missing in this discussion.

The freebore allows higher velocity with lower pressure than would otherwise be if it was conventionally throated. Its how Weatherby achieved the velocities they did with their cartridges. It cant be done with the same pressures with conventional throating.

From post 16

The free bore length for an M16 (aka 5.56mm) chamber is 0.0569" in diameter. (I believe length was what was meant)

The free bore length for a SAAMI .223 Remington chamber is . . . . 0.0250" in diameter. (I believe length was what was meant)

From Weatherbys site, FAQs. Click the question on freebore of Weatherby cartridges.

http://www.weatherby.com/support/faqs.html

Weatherby forum, discussing standard vs Weatherby throat/freebore

http://www.weatherby.dk/showthread.php?2808-Weatherby-Freebore

Sound familiar regarding different loads and pressures?

 

[Bart B.]

Depending on the case, powder and primer used along with the chronograph setup, a given cartridge and bullet can have a wide range of muzzle velocities with the same peak pressure. This is why comparing cartridge A to cartridge B will be skewed in results depending on conditions 1 through 10 with each. Some of those conditions are the way the test barrel's held as well as its bore and groove diameters.

When comparing two system against each other, it's best to change only one thing at a time. Most cartridge comparisons don't do this, so results are skewed by changing more than one thing at a time.

 

[denton]

The throating of the barrel.

I don't think that explains the difference.

Just extending the freebore on rifle does not increase muzzle velocity. In fact, if you don't change the load, it decreases MV a bit. Ackley did freebore tests and came away unimpressed with the results.

A long freebore allows you to seat bullets farther out, increasing case capacity, and allowing more powder without increasing peak pressure.

And we've established that the military isn't doing that.

The only remaining solution I can find is that military 5.56x45 is loaded to higher pressures than the SAAMI specification.

 

[Bart B.]

Denton, did you read my post #31? The 114 psi higher pressure of the NATO round is insignificant. There's a couple thousand psi spread across any lot of both.

Interesting information

http://www.luckygunner.com/labs/5-56-vs-223/

 

[bfoosh006]

"Quote:
How, then, does M193 get more speed out of a 20" barrel than the SAAMI spec for 223 out of a 24" barrel? I can't reconcile your statement with that fact.

The throating of the barrel. The part many seem to be missing in this discussion.

The freebore allows higher velocity with lower pressure than would otherwise be if it was conventionally throated. Its how Weatherby achieved the velocities they did with their cartridges. It cant be done with the same pressures with conventional throating.

From post 16

Quote:
The free bore length for an M16 (aka 5.56mm) chamber is 0.0569" in diameter. (I believe length was what was meant)

The free bore length for a SAAMI .223 Remington chamber is . . . . 0.0250" in diameter. (I believe length was what was meant)

From Weatherbys site, FAQs. Click the question on freebore of Weatherby cartridges.

http://www.weatherby.com/support/faqs.html

Weatherby forum, discussing standard vs Weatherby throat/freebore

http://www.weatherby.dk/showthread.p...herby-Freebore

Sound familiar regarding different loads and pressures?
__________________
"It amazes me that people "think" themselves into helplessness."
Bartholomew Roberts

"...always endeavour to raise your own standards."
Arfin Greebly

Isn't it amazing how many people post without reading the thread?"



This....

If you jam the typical 5.56 load into a .223 spec chamber... you will cause increased pressure.

Will it blow up a rifle ?.. maybe not.

Will you get sticky extraction or other un-wanted pressure related results.. probably


The various manufacturers have tested this issue many times.

If you want a rifle that can safely fire both 5.56 and .223... then buy one chambered in 5.56 or .223 Wylde ( the Wylde has a throat length in between )

 

[bfoosh006]

Bart B .... not trying to be difficult.. but the Nato testing is measured at the case mouth.....unlike your example.
Maximum pressure (EPVAT)
430.00 MPa (62,366 psi)

And IMHO... this is where the "longer freebore / throat" come into play.


NATO EPVAT testing procedures for the "NATO rifle chamberings" require the pressure sensor or transducer to be mounted ahead of the case mouth.

I would be very interested in see a NATO EPVAT test of common .223 ammo in a 5.56 chamber..... as well as 5.56 ammo in a .223 chambered rifle.

 

[sirgilligan]

Some differences in load data:

RAMSHOT TAC
5.56 NATO
BW Make Start Vel Max Vel PSI CIP COL
62 MIL M855 23.6 2,940 26.2 3,219 62,350 2.260
77 SIERRA HPBT MK 22.3 2,648 24.8 2,902 61,500 2.260

.223 REM
BW Make Start Vel Max Vel PSI COL
62 MIL M855 22.5 2,800 25.0 3,078 54,947 2.260
77 SIERRA HPBT MK 21.1 2,483 23.4 2,759 54,500 2.260

 

[bfoosh006]

Quote.....

"The 5.56 mm NATO chambering, known as a NATO or mil-spec chamber, has 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 Remington 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) or the ArmaLite chamber, which are designed to handle both 5.56×45mm NATO and .223 Remington equally well. The dimensions and leade of the .223 Remington minimum C.I.P. chamber also
differ from the 5.56 mm NATO chamber specification."


"Using 5.56 mm NATO mil-spec cartridges (such as the M855) in a .223
Remington chambered rifle can lead to excessive wear and stress on the rifle and even be unsafe, and SAAMI recommends against the practice."


So even SAMMI warns against it.

 

[Bart B.]

bfoosh006,

The USA military pressure standard is not the same as NATO; same round gets different pressure level numbers across each. I thought I'd covered that.

https://en.m.wikipedia.org/wiki/Small_arms_ammunition_pressure_testing

This thing in this thread has taken on the same confusion and terminology issues when every one called copper units of pressure systems "psi" for the 7.62 NATO round as 50,000 of them for USA military use, 52,000 for commercial use. When they switched to piezo transducer systems, 62,000 was the number used with units called psi.

 

[bfoosh006]

Quote.....

A SAAMI spec .223 Remington chamber will have a shorter leade with a sharper angle to the leade and a shorter amount of effective freebore than a 5.56mm NATO chamber. The freebore itself will also be narrower in the .223 Remington chamber.



Quote.....



Here's a very interesting quote posted by Ned Christiansen on M4carbine.net:


". . . In short, you can safely fire all 5.56 AND 223 ammunition in a gun properly chambered for 5.56. You MUST NOT fire 5.56 ammunition in a 223 rifle. As case in point, I fired XM193 5.56 ammunition in a 223 test barrel with average pressures (conformal transducer) of 72,550 psi, and peak pressure registered at 76,250 psi. . ."

Since the SAAMI MAP for the .223 Remington is 55,000 PSI, that puts XM193 fired from a minimum spec .223 Remington chamber at 17,550 PSI over the maximum.


(The following is just a generalization to give a graphical demonstration of concept. DO NOT hold me to the exact numbers as they are not correct and they ignore the difference due to the different methods used to measure chamber pressure.)

Consider the left graph pictured below; M193 fired in a 5.56mm chamber. The pressure is within the MAP limit. Now, take the exact same round, (same powder, same charge of powder) and fire it from a .223 Remington chamber; pictured in the right graph below.

Because the .223 Remington chamber has a shorter and sharper angled leade compared to the 5.56mm chamber as well as a shorter effective free-bore, the bullet engages the rifling sooner in the .223 chamber than it would have in a 5.56mm chamber. This causes the pressure to rise faster, peak sooner and reach a higher (and per SAAMI, unsafe) level than it would have if the round had been fired from a 5.56mm chamber.

 

[RecoilRob]

Having reloaded a crap-ton of 5.56 once-fired cases....they pretty much all needed their OAL trimmed down to meet .223 specs. And interestingly enough, the trimming pretty much removes the crimped area of the neck. Considering this, I do believe that factory 5.56 cases will pinch their crimps into a tight .223 chamber leading to higher pressures. I know the listed OAL is shared for both 5.56 and .223...but in reality the cases of the former are quite a bit longer in the necks than the latter in my experience.

 

[lysanderxiii]

I believe that you are correct. I temporarily cross-combobulated cartridge length with chamber length.



The whole EPVAT/SAAMI pressure spec thing is a bucket of worms. Measuring pressure at the middle of the cartridge with a perforated case gives one result, measuring with a non-perforated case gives another, and measuring at the case mouth gives a third. As nearly as I can determine, you cannot simply dial in the offset from the pressure containment of non-perforated brass and get the case mouth figure. The difference between perforated an non-perforated mid-case measurements tends to be about 5,000-7,000 PSI because the brass bears some of the gas containment load.



The military spec for M193 is 3,250 FPS from a 20" barrel. The SAAMI spec for 55 grain 223 Rem is 3050/3215 FPS from a 24" barrel. So it must needs be that military 5.56x45 is loaded hotter than SAAMI specs.

A transducer sees a pressure and just gives you a voltage, nothing more.


You have to assign a pressure level to that voltage in order to get a calibrated pressure gauge. This is why there is such thing as reference ammunition, ammunition that is manufactured to very tight pressure specification, so you can calibrate your transducer.


A conformal transducer can be calibrated to match a pierced case transducer by firing two rounds (or, a good statistical sample) with the same pressure one with a conformal and one with a pierced case and comparing the voltage. If the reference pressures are 52,845 psi, and the pierced case measurements are 25 mV, and the conformal transducer measurements are 23.5 mV then you have calibrated your conformal gauge to a known standard.


Preferably you do this at several pressure levels to establish the offset and divergence, etc.


Ideally, conformal gauges need to be calibrated for each brass lot, for the reasons you stated, but even without doing so, testing of conformal gauges, on average, showed at most a variation of +/- 5% across about ten domestic and foreign ammunition brands that about 2500 psi for a 50,000 psi cartridge.


Similarly you can do the same with case mouth and conformal or case mouth and pierced case transducers.


And military M193 ammunition is not loaded to 3250 fps Vm, it is loaded to 3165 +/- 40 fps at 78 feet from the muzzle. It used to be 3250 +/- 40 fps at 15 feet.


However, pressure depends on the burn rate of the propellant. The M193 cartridge you quoted has a maximum allowable average pressure of 55,000 psi, which can be lower than SAAMI lot average pressures. So even taking into account for the differing locations of the transducer, there is not much difference, when fired from their respective chambers.

 

[lysanderxiii]

I don't think that explains the difference.

Just extending the freebore on rifle does not increase muzzle velocity. In fact, if you don't change the load, it decreases MV a bit. Ackley did freebore tests and came away unimpressed with the results.

A long freebore allows you to seat bullets farther out, increasing case capacity, and allowing more powder without increasing peak pressure.

And we've established that the military isn't doing that.

The only remaining solution I can find is that military 5.56x45 is loaded to higher pressures than the SAAMI specification.

Not true.

Throating has been proven to change Vm significantly.

To visualize, imagine the difference in effort required to dent something by simply pushing on it versus throwing it at something....

 

[boom boom]

My rifles have 5.56 chambers but I shoot .223 in them normally. Biggest reason is that .223 ammo normally does not have crimped primers and I do not need the extra little bit of extra velocity/pressure for punching paper at 25 to 100 yds. I also find .223 a bit cheaper online than 5.56.

As Bart B. says above, part of the issue is that it is a multi variable problem--different ammo makers, different powders, different primers, different rifle chambers/headspace, bullets/jacket composition, different case brass thickness, crimping, differing means of measuring pressure, rifle gas length system, etc. You have to hold all other variables constant to effectively measure one variable. Otherwise, the discussion just devolves down to raw opinion or at best an informed opinion.

 

[denton]

lysanderxii, I think we can probably have a long and profitable conversation about these topics, but not this week. I'm doing 14 hour days delivering Six Sigma Black Belt to a US government agency, and it's about like being on a submarine for a week.

When I surface, I'll jot down some food for thought and send you a PM. That's probably a better channel for our communication.

In the meantime, here is some experimental data on freebore from P O Ackley. Holding other factors constant, extending freebore in every case reduces pressure and muzzle velocity.

 

[barnbwt]

Is anyone actually cutting barrels in anything but 5.56 at this point (outside custom match chambers)? NATO FMJ is such a huge focus of the market anymore, that the 'inability' (alleged inability) so safely chamber the gewd stuff in your 'civilian' m4gery is a major turnoff, if not outright liability.

And of course, the confusion between the reason for the two as far as ammo, vs. chambers. 5.56 is a series of service-specific loads defined by NATO, which obviously don't include your super heavy Nosler hunting bullets, so '223' serves as the catch-all for these non-military-standard options; that makes sense, at least to me. Chambers is where the distinction is truly without any need for a difference at this point; they ought to just classify them like machine screw threads in terms of clearance/tolerance; loosest can be your NATO machinegun chambers, intermediate your rifle barrels, and tightest your match chambers with a short leade to engrave the bullet upon (and of course custom stuff in addition to that). Between all the types of chambers and reamer manufacturers, the overlap is beyond significant; they are the same chamber cut to different clearances.

Everyone knows it's a risk factor to shoot hotter ammo in a tight chamber, or really cram a fat-ogive bullet onto a barrel's lands; the difference between 223 and 5.56 is no different from what I've been able to determine (and even then, the 'risk factor' is largely theoretical and marginal as opposed to imminently dangerous)

TCB