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This is an old article from Gun Digest that that explains how the Armalite M16 came to be it also points out some very common safety defects. I am sure these defects are in the barrel of as many as 1 in 7 5.56 rifles. I found the article to be entertaining and informative. I don't even like AR15 rifles or the .223 cartridge.

Here is a snippet from the article: At my latest LEO patrol rifle class, I chamber-gauged the two dozen rifles the officers had brought. All but two were marked “5.56.” One of those was an M16A1 and the other had a completely unmarked barrel. Of the 24 rifles, six failed the .223/5.56? Gage test. Two of those were not just .223-chambered, but clearly on the small side of the dimensions, as I had to use force to remove the Gage.

http://www.gundigest.com/ammunition-reviews-articles/223-vs-5-56/4
 

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My Dad's two Bushmasters are .223 marked, Busmaster says not to use 5.56 in them.

My two "surplus" uppers, an M16 and an M16A1 eat all of it. Both would probably fail a Go - No Go gauge, which is why the military rifle gurus say to only use a "Field" gauge on military rifle chambers. A perfectly good rifle will probably fail a "match chamber" gauge test but pass a Field Gauge test. I have a 5.56 field gauge somewhere, haven't used it in years.

By failing the gauge I assume the chambers were oversized? Or the one was too tight? Manufacturers try to account for the fact that civilians will use the cheapest available .223 or 5.56 available. Wolff steel case is marked .223 but the spent shells would stick in my .223 marked AR180b.......my M16 "clone" eats steel case all day long thanks to a sloppy military chamber.

Military chambers are notorious for being "sloppy", USGI M16's and M4's have sloppy chamber tolerances, a combination of mass produced barrels made by the lowest bidding contractor and they are also left "sloppy" to account for dirt, grime, dirty ammo, and mass produced Lake City and other types of 5.56 that may be slightly out of spec.....also that US military troops train with blanks that are horribly dirty and probably not made with the same case size QC as live ammo.......also probably accounted for is the fact that we will probably give these rifles away to 3rd World armies like Afghanistan or South American countries who will use crap indigineously produced ammo with varying degrees of being out of spec. The US Govt. isn't interested in match grade chambers, they want the darn things to work.

Chamber sizes are strange, even some of my revolvers have chambers within the same gun, where one chamber will be a bit "sticky" to extract and the others are fine.....probably one chamber is less well polished or maybe .001-.002 tighter. These mass produced guns are made to a price point and as long as they work they are released, AR15's are no exception. If the chamber is in spec, it will pass test firing and QC and get boxed up. Manufacturers aren't about to scrap a good barrel over a little tightness or slop that most people won't even notice.......unless you're paying $2-3,000 for a custom high-end AR.
 

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The AR & SR556 are both chambered for. Drum roll-- 5.56. I guess since they put it in the name it was a good idea.

Some of these shops were cranking out rifles with whatever they could get their hands on during the big sales spike and parts shortage.
 

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.223 vs 5.56mm

I have had three Mini-14s (I even had a GB model, bayonet lug, flash suppressor and factory 20 round magazine).
I have used .223 and 5.56mm in all of them.
I currently have a model #195.

Here is a statement from the owner's manual:


Pretty clear to me.
Sameo sameo!
 

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The problem is that .223 chambers are cut to SAAMI specs and the 5.56 chambers are cut to NATO specs which accounts for a longer throat for longer bullets. Also .223 pressures are 50,000 CUP max pressure while the 5.56 pressures are 60,000 CUP pressures.

The censuses is that 5.56 should never be fired in rifle chamber in .223 to SAAMI specs. However, .223 can usually be fired in a 5.56 chamber although SAAMI says only fire ammo in the right designated chamber.
 

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The issue is well overblown. In an AR only the Bushmaster Carbon 15 and perhaps some varmint style rigs are spec'd as .223 only. There's plenty of hybrid chambered barrels out there (.223 chamber specs with 5.56 throats).

In most modern bolt actions of sound design it's no problem. Extraction may be a little sticky with 5.56 but if it's a quality firearm no harm will come of it.
 

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Somewhat on topic... What about .223 vs 5.56 in terms of ballistics themselves? For example, would a 55 grain .223 perform the same as a 55 grain 5.56 shot out of the same firearm?
 

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The issue is well overblown. In an AR only the Bushmaster Carbon 15 and perhaps some varmint style rigs are spec'd as .223 only. There's plenty of hybrid chambered barrels out there (.223 chamber specs with 5.56 throats).

In most modern bolt actions of sound design it's no problem. Extraction may be a little sticky with 5.56 but if it's a quality firearm no harm will come of it.
One would think so with a modern bolt action but many manufacturers recommend against it. I guess it all boils down to, "Do you feel lucky, well do ya?"
 

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Somewhat on topic... What about .223 vs 5.56 in terms of ballistics themselves? For example, would a 55 grain .223 perform the same as a 55 grain 5.56 shot out of the same firearm?
There's a lot of variables there. A all copper match bullet probably not as that bullet would need a long throat and a fast twist. But standard size copper/lead bullet would have to jump the throat to the rifling. A fast twist probably would not have as much effect on the bullet. In fact, many .223 rifles are going to fast twist barrels because of long bullets made of the all copper as copper is lighter than copper/lead bullets.

So to answer your question an all copper bullet out of either with a fast twist would work the same I would think.
 

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.223 vs 5.56



The neck might be a bit thicker on the 5.56mm and the primers a bit less sensitive (machines guns you know) but, if the cartridge chambers and the shell ejects without difficulty after firing there will be no problems. Now, if you have a slow twist, 1-14, 1-12, 1-10 then the heavy bullets loaded in the 5.56mm will not stabilize. That is why the Ruger Mini-14 went to a 1-7 twist.

I say, chamber a 5.56mm by hand (using your fingers).
If it chambers without difficulty and you can remove it easily then all is good.

If you have problems you may send your commercial ammunition to me and I will shoot it.:D
 

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But the internal dimensions between the two cartridges are different. 5.56 cartridges usually have thicker internal construction but not always. The problem also with 5.56 ammo is that many countries that use the 5.56 for their military produce their own 5.56 to their own specs which may not be to NATO specs and certainly not up to SAAMI specs. Heck, from my research even NATO countries which are suppose to all follow the NATO specs do not do so.

My research has shown one can usually fire .223 in 5.56 but should never ever fire 5.56 in .223 unless the manufacture says it's okay to do so.

But heck, unless you are shooting next to me fire whatever you want to fire in the sucker I don't care.
 

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There's a lot of variables there. A all copper match bullet probably not as that bullet would need a long throat and a fast twist. But standard size copper/lead bullet would have to jump the throat to the rifling. A fast twist probably would not have as much effect on the bullet. In fact, many .223 rifles are going to fast twist barrels because of long bullets made of the all copper as copper is lighter than copper/lead bullets.

So to answer your question an all copper bullet out of either with a fast twist would work the same I would think.
Let's say we are talking just cheap target brass ammo. Is the 5.56 loaded hotter/have a higher velocity?
 

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I don't know for sure. Remember, military 5.56 is also used in machine guns. Military 5.56 have less powder capacities, usually, than .223 brass.

Civilian rifles set up for .223 SAAMI specs will have shorter throats than military 5.56 throats in military rifles and that is really where the problems can come from, as I understand it, from higher pressures than the rifle was designed for in the civilian rifle.

Civilian rifle makers are now starting to allow for the longer throats using "modified" throats, .223 Wylde, etc.

https://en.wikipedia.org/wiki/.223_Wylde

Here might be some useful info:

5.56 vs .223 - What You Know May Be Wrong - LuckyGunner.com Labs

.223 Remington vs. 5.56 NATO: What You Don't Know Could Hurt You - Bearing Arms - Remington

American Rifleman | .223 Remington Vs. 5.56: What's in a Name?

Is There a Difference Between .223 and 5.56? | The Arms Guide

Well this ought to get you and everybody going.

As I said earlier I would not fire a 5.56 in a .223 chamber unless the manufacturer of the rifle said it's okay to do so. This is my opinion and my opinion only.
 

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I don't know for sure. Remember, military 5.56 is also used in machine guns. Military 5.56 have less powder capacities, usually, than .223 brass.

Civilian rifles set up for .223 SAAMI specs will have shorter throats than military 5.56 throats in military rifles and that is really where the problems can come from, as I understand it, from higher pressures than the rifle was designed for in the civilian rifle.

Civilian rifle makers are now starting to allow for the longer throats using "modified" throats, .223 Wylde, etc.

https://en.wikipedia.org/wiki/.223_Wylde

Here might be some useful info:

5.56 vs .223 - What You Know May Be Wrong - LuckyGunner.com Labs

.223 Remington vs. 5.56 NATO: What You Don't Know Could Hurt You - Bearing Arms - Remington

American Rifleman | .223 Remington Vs. 5.56: What's in a Name?

Is There a Difference Between .223 and 5.56? | The Arms Guide

Well this ought to get you and everybody going.

As I said earlier I would not fire a 5.56 in a .223 chamber unless the manufacturer of the rifle said it's okay to do so. This is my opinion and my opinion only.
I've read the first 3. I will check those other two out when I get home from work. The problem I am running into is those articles explain the differences but they don't seem to touch on anything after the bullet actually leaves the barrel. Just everything that happens before that...

Either way, mine is chambered for 5.56 so shooting either is no issue to me. I am just curious because Federal American Eagle .223 55 grain and Federal American Eagle 5.56 55 grain can be had for the same price in my area. I was curious if possibly one would be considered more bang for your buck than the other...
 

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When NJ banned AR-15's and a whole host of other semi auto's, the Only black rifle one could get was a neutered Colt Target model with 16" bbl, fixed stock, target crown, 223 ONLY chamber, no bayo lug and I think for a while they tried to force people to register them. The reason for 223 only was it is a sporting round, not a evil warmonger NATO round. It was a politically correct round, well, as politically correct a cartridge can be anyway.

In a way, I think the AWB helped spur the success of 223.

I split the difference between the two chambers when I built my SPR with a match grade 223 Wylde chamber.
 

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Discussion Starter #18
The 223 wylde eliminates most of the tooling problems that arise when cutting a 5.56 chamber.

If you read the article closely it says that damage is likely to occur when shooting long strings that heat the metal beyond the what is considered a normal operating temperature. Otherwise you will be just wondering why my accuracy sux with 5.56 ammo. We are not talking about a lot of expensive tools to remedy this mistake in tooling. You can turn the reamer with your bare hands.
 

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The issue is well overblown. In an AR only the Bushmaster Carbon 15 and perhaps some varmint style rigs are spec'd as .223 only. There's plenty of hybrid chambered barrels out there (.223 chamber specs with 5.56 throats).

In most modern bolt actions of sound design it's no problem. Extraction may be a little sticky with 5.56 but if it's a quality firearm no harm will come of it.
Wait, what? My Bushmaster Carbon 15 is spec'd for both and even says so on their web page. https://www.bushmaster.com/firearms/carbon_15.asp maybe they have or have had a variant that is .223 only but that is certainly not true of the entire Carbon 15 product line.
 
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