Conventional Wisdom on .223 and 5.56?

Spats McGee

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TLDR: A buddy of mine made some remarks a few days ago that have me questioning the conventional wisdom on .223 and 5.56.

Ok, so here's the TL part: For decades, I've heard the conventional wisdom that "you can shoot .223 in a 5.56 rifle, but not the other way around, because of pressure issues." When it comes to guns, I generally follow conventional wisdom unless and until I can do sufficient research to determine for myself that it's wrong. Given that I'm a lawyer and not an engineer, that doesn't happen often. So I recently bought a Howa Mini in .223. It's a nice rifle, but historically, I've never really kept .223 on hand. I've had a couple of 5.56 rifles over the years, and generally bought 5.56 ammo for them. I do have some loose .223/5.56, and there's likely some of each mixed in those batches together. The odds of me successfully sorting out the .223 from the 5.56 rapidly approaches zero. So ..... I was left with a dilemma: (a) buy .223 specifically for the Howa; (b) sell the Howa and buy something in 5.56; or (c) risk shooting 5.56 ammo out of a perfectly good .223.

So I mentioned this to my buddy. He tells me not to worry about it, nothing bad will happen. Now, had this been some Nine-Fingered Ned with a history of accidentally blowing stuff up, I'd have smiled, nodded, and ignored him. But he's a very good gunsmith, and knows far more about firearms than I do. And then he said that gun companies won't build a .223 that is so ammo sensitive as to be dangerous if you're shooting 5.56, or damaged by it. He says that the liability of building a rifle that will chamber two different rounds, only one of which is safe to shoot, is a lawsuit waiting to happen. Now he's talking my language. We all know I'm no engineer, but I do have a basic understanding about how litigation costs can drive product design... And if I worked at a gun company, there's no way I would approve such a thing.

So I guess my question is this: Have y'all ever seen a .223 rifle that was actually damaged by shooting 5.56? And I mean without other complications, like a double-charge of powder, a squib or a manufacturing defect. Damage or danger directly traceable to ammo selection.
 
He generally right. Most bolt action .223s built in the last 20 years or so will fire 5.56 without a hiccup. Where you're going to run into trouble is with much older guns, like 700s from the 60's and 70's, particularly with custom barrels. The leades on those are very short, and will cause pressure rises. Also, single shot break open .223s will tend to stick and/ open upon firing. I had 2 Handi-Rifles that did that with 5.56. The rifles weren't damaged, but I only fired a few to test whether they'd stick.
Here's a pictorial Gunny posted some time back that illustrates the differences between .223, .223 Wylde, and 5.56 chambers:

P_20190407_230237.jpg
 
I haven’t heard of anyone damaging a rifle by shooting 5.56 NATO ammo in a .223 chamber. My personal experience was long ago with a Savage light Varmint 110 in .223 Remington. I purchased many boxes of caliber 5.56 55 gr ball Winchester ammo from the White Elephant store in Spokane, Washington, because it only cost $2.99 for 20 rounds and shot it through my Savage. ( that price gives a hint as to how long ago this was) Never had an issue and reloaded the brass multiple times over the years.
 
As others have said, most 223 chambered rifles will actually have a chamber closer to 223 Wydle or 5.56. Manufacturers do this for safety and liability reasons knowing that people will shoot 5.56 from a 223 rifle. If you are in doubt then take a chamber casting to see what you have.

You can still find 223 rifles with a true to spec 223 chamber that can have issues when shooting 5.56 ammo. But most modern bolt action rifles will handle it. The last rifle I had with a 223 chamber was a H&R Handi-Rifle. And I did have issues shooting 5.56 ammo in it. The extra pressure from 5.56 ammo would cause the action to pop open when the rifle was fired.

When it comes to reloading, the only difference between 223 and 5.56 is the actual load data ie. powder charge. You can't always go by case weight or case volume (water volume) since there is a variance between manufacturers. I have seen 223 brass that was thicker and less volume than military issue NATO Lake City brass. One will use the same reloading dies for both 223 and 5.56.
 
OK, if I understand this correctly -- the difference is that "5.56" ammo is a hotter loading than ".223." The dimensions of the ammo are the same.

My only guns in this caliber are AR-15's, AR-180's, Daewoo's -- all automatics/semiautomatics. No bolt guns in this caliber.

Some of these semiautomatics are actually marked ".223 Rem." either on the lower receiver or on the barrel. Does that mean that they're chambered that way? It's not clear.

Has there ever been a problem firing military "5.56" ammunition in early AR's marked ".223 Rem."?
 
OK, if I understand this correctly -- the difference is that "5.56" ammo is a hotter loading than ".223." The dimensions of the ammo are the same.
Yes that is correct. both are the same as far as dimensions go. NATO spec 5.56 ammo is loaded hotter.

The reason for the 5.56 chamber is to deal with the extra pressure and also to function in dirty combat conditions.

To your last question, it will depend on the chamber and if it is cut/reamed to true 223 specifications or not. Shooting NATO spec 5.56 ammo in an AR with a true 223 spec chamber could lead to premature wear /breaking of the bolt lugs.
 
I ran into this situation with my CZ 600. It’s chambered in 223 Rem but all the ammo for that caliber I have is in 5.56 NATO.

I wasn’t going to cry about it or convince myself that any familiarity with firearms or cost and design means I know what the **** I’m talking about regarding pressure testing. I set about buying specific 223 Rem ammo.

Luckily for me, CZ explicitly states that my rifle can also fire 5.56 NATO. Bully for me. Does that mean anyone can extrapolate and infer a conclusion from my experience to support their view? Sure but it wasn’t explicitly stated for their rifle.
 
You're never going see a post WW1 firearm damaged from a few thousand PSI. The brass will show it. Failed primer pockets are the big indicator. Sticky bolts can happen, but in 5.56 you'll probably never notice. But if it does fail for any reason, the manufacturer will have a blown out 5.56 head lodged in the action , a stamp on the barrel saying ".223 rem" a page on the manual sayin no, and expert witnesses from SAAMI on their side.
 
.223 damaged by 5.56? No, I have never seen that. I did have a .223 rifle that would malfunction with just about ever 5.56 I put through it. Half the time I would have to mortar the case out of it.

FYI, the lower was marked 5.56. Under the handguard was stamped .223 on the barrel. Guess which one was telling the true story.

I haven't, but most gun owners are mindful about safety.

50.01%? Kidding aside, I have been present for 2 guns that blew up over the years, one with vintage military ammo and one with reloads. I have been present at least twice when folks have fired 9mm out of a .40 cal. I have been present for countless squibs, weak charges, and over charges. I have been down range and have seen others down range when somebody started shooting from the firing line. I was on my own property when the neighbor guests decided to use it for a backstop. Most gun owners may be mindful about safety, but a lot of mistakes get made, none-the-less. If it is likely or probably that a 5.56 would blow up a .223 rifle, I think we would have several examples of it by now.

Some of these semiautomatics are actually marked ".223 Rem." either on the lower receiver or on the barrel. Does that mean that they're chambered that way? It's not clear.

That is what they the marking is supposed to mean, generally speaking.

Many manufactured complete guns or lowers that are intended to be mated with the appropriate barrel, will have the caliber stamped on the lower. All my AR15 lowers are stamped .223, .223 wylde, or 5.56 and most were purchased as complete rifles. I always look to see how the barrel is stamped after my experience above, however, which was on a Frankenstein gun. Plus now, most of my .223/5.56 lowers are on 6.5 Grendels, so what the lower receiver says is not relevant.
 
Before the internet they were considered interchangeable.

There are minor differences in chamber dimensions with 5.56. They have slightly loose tolerances to promote reliability. 5.56 CAN be loaded to slightly higher pressure. But no manufacturer loads any cartridge right to the limits. Virtually all factory loaded 5.56 ammo is still within pressure limits for 223. The external dimensions of both cartridges are identical.

If you were to get a 5.56 cartridge loaded right to the max AND load it in a 223 chamber cut to minimum specs you could get a slightly over pressure round. The odds of that happening are exceedingly small and would never be a problem in a modern bolt rifle.

The only issue is that autoloading rifles need chamber pressures to be within a certain range in order to function properly. Too low and it won't cycle. Too much pressure and you will eventually damage the operating system. Currently I don't know of a single autoloading rifle with a 223 chamber. The very early Ruger Mini-14's had 223 chambers and that is the only rifle that could potentially be an issue.

FWIW, this is a much larger issue with 30-06 and nobody ever talks about it. The WW-1 30-06 loading was a 150 gr bullet at 2700 fps. WW-2 was 2800 fps. Common commercial hunting loads are now 2900 fps and some specialty factory loads and handloads can be as much as 3100 fps.

That's quite a range and most current commercial loadings will eventually destroy a Garand or any other semi-auto rifle designed for the 2800 fps load. If you own a semi-auto 30-06 you REALLY have to worry about the loads much more so than 223/5.56.
 
My original duty rifle Bushmaster would pop primers with M193. Especially if the rifle got really hot. Not ever shot, but a few times every magazine.

We did have one rifle get the inside of the upper receiver scratched up pretty good when the primer got in between the BCG and receiver wall. While the 223 chamber did cause the incident to happen, I dont know if Id say the act of firing the 5.56 in a 223 damaged the gun itself. We had several guns go down with primers in the trigger group, but that was the only one I know of that was actually "damaged".
 
Before the internet they were considered interchangeable.

There are minor differences in chamber dimensions with 5.56. They have slightly loose tolerances to promote reliability. 5.56 CAN be loaded to slightly higher pressure. But no manufacturer loads any cartridge right to the limits. Virtually all factory loaded 5.56 ammo is still within pressure limits for 223. The external dimensions of both cartridges are identical.

If you were to get a 5.56 cartridge loaded right to the max AND load it in a 223 chamber cut to minimum specs you could get a slightly over pressure round. The odds of that happening are exceedingly small and would never be a problem in a modern bolt rifle.

The only issue is that autoloading rifles need chamber pressures to be within a certain range in order to function properly. Too low and it won't cycle. Too much pressure and you will eventually damage the operating system. Currently I don't know of a single autoloading rifle with a 223 chamber. The very early Ruger Mini-14's had 223 chambers and that is the only rifle that could potentially be an issue.

FWIW, this is a much larger issue with 30-06 and nobody ever talks about it. The WW-1 30-06 loading was a 150 gr bullet at 2700 fps. WW-2 was 2800 fps. Common commercial hunting loads are now 2900 fps and some specialty factory loads and handloads can be as much as 3100 fps.

That's quite a range and most current commercial loadings will eventually destroy a Garand or any other semi-auto rifle designed for the 2800 fps load. If you own a semi-auto 30-06 you REALLY have to worry about the loads much more so than 223/5.56.
I will agree that most commercial loaded 5.56 ammo is not hotter than 223 and that is for liability reason. Now when we start talking about military ammo loaded to NATO specs then yes NATO 5.56 is loaded hotter.
 
I've heard the conventional wisdom that "you can shoot .223 in a 5.56 rifle, but not the other way around, because of pressure issues."
Potential pressure issues, correct.

A lot of folks have shot a lot of 5.56 in .223 chambers, and have gotten away with it. Me? I have a choice, so I wouldn't do it.

And anyway, you're often times shooting 5.56 in ARs or Mini 14s, and similar guns with 5.56 chambers that aren't going to be shot in a serious match, right?

Your match guns have match grade barrels with match chambers and want better ammo than 5.56 ammo. Even if it's an AR, your shooting match grade ammo from a trusted commercial source or you hand loaded it, at .223 pressures.

So for me it's a non issue/problem.
 
I haven’t heard of anyone damaging a rifle by shooting 5.56 NATO ammo in a .223 chamber. My personal experience was long ago with a Savage light Varmint 110 in .223 Remington. I purchased many boxes of caliber 5.56 55 gr ball Winchester ammo from the White Elephant store in Spokane, Washington, because it only cost $2.99 for 20 rounds and shot it through my Savage. ( that price gives a hint as to how long ago this was) Never had an issue and reloaded the brass multiple times over the years.
The good old white elephant, usually the cheapest place in town for firearms & ammo
 
He says that the liability of building a rifle that will chamber two different rounds, only one of which is safe to shoot, is a lawsuit waiting to happen.

Yet the 300 blk still exists…

So I guess my question is this: Have y'all ever seen a .223 rifle that was actually damaged by shooting 5.56?

No.
 
I’m afraid I know very little about 300 blk. I take it there is another round that could fit in the same chambers?

Yes., it’s made from .223 brass cut below the shoulder, with a bullet that becomes a bore obstruction.

449AF238-40CB-4778-9709-5403B9AA092F.jpeg

 
300 AAC Blackout is certainly a danger in a 223/556 gun. But not every round of 300 BO creates that dangerous conditions. My subsonic loads (and many commercial subsonic loads) will not let the bolt close no matter how hard you try. The long heavy bullet sets back solid on the powder charge long before the bolt can close. Often with the really light bullets and small charges of fast powers the bullet will seat completely into the case body and then case will go too deep into the chamber to head space and the firing pin cannot reach it. So the danger is real but only a subset of 300 BO ammo creates the proper head spacing to cause this issue. This is something you can safely test and know ahead of time. In addition to taking precautions to be sure you don't mix ammo up you can select ammos that are unlikely to cause the issue if you want to be double safe.

Since I use 300 BO almost exclusively as a subsonic gun I feel pretty secure that I will not have any issues. My subsonic loads will not chamber in a 223, I keep ammo separate both in storage and use separate dedicated magazines (my one subsonic load requires 300 BO specific magazine to feed into the magazine). And I rarely take my 223/556 guns out anymore, except for the occasional carbine or 3-gun match, having found other cartridges in the AR I like better for general and hunting uses. Just being aware of the potential problem goes a long way to avoiding it.
 
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TLDR: A buddy of mine made some remarks a few days ago that have me questioning the conventional wisdom on .223 and 5.56.

So I guess my question is this: Have y'all ever seen a .223 rifle that was actually damaged by shooting 5.56? And I mean without other complications, like a double-charge of powder, a squib or a manufacturing defect. Damage or danger directly traceable to ammo selection.

No, I have never seen a 223 damaged by Nato ammo. And I have shot a good bit of it in my Remington 700. Mostly to get fire formed brass. I never even saw anything on the fired brass that worried me. But I rebarreled that rifle last year and the new barrel has a tighter chamber and a shorter leade. So it will only see 223 ammo. For me, its kind of a mute point as I have not bought any factory .556/223 ammo in like forever!

Like JMR40 said, "before the internet they were considered interchangeable".

I'm not challenging anyone that has had a negative experience, just stating my experience. Apologies if this came off that way!
 
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