Truth or Fiction - 5.56x45 same as .223Rem?

So I'm in a gun store. A customer is asking if the 5.56 ammo that is on sale is the same as .223Rem. The salesman says, "Oh yeah, they're exactly the same." Um...what?

Now I usually leave gun store salesman stupidity alone and chuckle from afar, but I don't want to see anyone get hurt. Therefore, I speak up and say they're not the same and that 5.56 has a higher chamber pressure. The first salesman said, "Oh, really?" and then we were interrupted by yet another salesman who stated loudly, "No! They're exactly the same. I spoke with Federal and they told me they are the same." I left it alone at that point. I did note that the customer didn't buy any ammo.

Not one to let things go easily, I did some research. I found this:
.223Rem= 58,500psi (SAAMI specification which uses the SATCP testing methodology)
5.56x45= 62,336psi (using the EPVAT testing methodology)

Because there is no SAAMI spec for 5.56x45, we don't really know how the two rounds compare. The difference in testing could account for the difference in stated chamber pressure.

Well, I didn't stop there. I went to the Federal website where I found this:

Federal said:

Both of these popular calibers feature a .224-inch-diameter bullet and an identical overall length. However, the throat length for 5.56x45mm is longer than that of 223 Rem. As a result, you can safely shoot 223 ammunition in a 5.56 chamber, but not 5.56 in a 223 platform, as it can result in excessive pressures upon ignition.

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Now why would Federal tell the salesman one thing when it clearly states something else on the website? Also, why would they label the box 5.56 NATO if it meets the .223Rem standard? The salesman couldn't possibly have told me an untruth, could he? No, gun store salesmen are always well trained and super knowledgeable and would never spout any FUD.

OK, seriously, do you guys know anything more about this? I've always been told that a gun chambered in 5.56 can shoot either while a gun chambered in .223 can only shoot .223 and that shooting 5.56 could result in damage to the gun and a possible catastrophic failure due to over pressure. That is always what I've gone by. Have I been believing a myth or am I correct in my belief?

Rastoff said:

OK, seriously, do you guys know anything more about this? I've always been told that a gun chambered in 5.56 can shoot either while a gun chambered in .223 can only shoot .223 and that shooting 5.56 could result in damage to the gun and a possible catastrophic failure due to over pressure. That is always what I've gone by. Have I been believing a myth or am I correct in my belief?

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You are correct. Those salespeople need retraining, lest they generate a huge civil liability for the store

My 2 Cents!

I can not answer the why question but I do know that your right.
The 5.56 is loaded to higher pressures. The chambers are very close but the free bore is longer on the 5.56.

Both are safe in the 5.56 chamber but not in the reverse. That being said I do realize that many people ignore these warnings.

I actually know of only one rifle that would not do well with 5.56. It was a 788 Remington in .223. It had a very short throat and if 5.56 ammo was fired in it it locked the bolt so that it had to be hammered open.

My M&P 15 OR is 5.56 so I can and do shoot both. With bulk .223 being available cheap why risk it? Geo. T.

The guy either made up that Federal told him that to try and make a sale on the ammo, or the person he spoke with from Federal was ill informed on the subject and told him wrong.

It was a good sale on the ammo. Federal American Eagle 5.56 NATO, 500 rounds for $189. I probably should have picked some up, but I was there to buy a gun and was short on funds.

I have a zip lock bag with about 500 spent brass from both 5.56 and .223. You can clearly see thru bag which is 5.56 and which is the .223.
Why some salesmen will tell you they are exactly the same is the question of the ages. Either they truly are stupid, or have been told by the boss there is no difference. Either way, it can get someone hurt.

Just because you work in a gun store doesn't mean you know a thing about guns.

My understanding is with you Rastoff. 5.56 is a little hotter. Yes, .223 in a 5.56 gun is fine. Will shooting a few rounds of 5.56 in a gun chambered for .223 blow it up? Probably not, but I don't like being a crash test dummy.

Shoot what your gun is chambered for. Or, in the case of a 5.56, shoot a lesser round that will function.

I have an old 38 Special revolver. Manual says NOT to shoot +p ammo in it. Never felt the desire to test their instructions.

Have seen a lot of stupid in gun shops. I normally don't say anything, but something I know might be unsafe, I probably would say something.

Nope, you're pretty much correct. A 5.56 NATO leade is longer than that of the .223 Remington. You can shoot .223 in the former, but not vice versa.

As far as what happens if you do it anyway, in many cases it results in blown primers which choke up the action. I haven't heard of any actual KBs resulting from it, but I wouldn't say it's impossible.

Is there a similar difference between 7.62x51mm and .308 Win.?

Larry

lebomm said:

Is there a similar difference between 7.62x51mm and .308 Win.?

Larry

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As I understand it, 7.62x51 and .308Win are the same. Does anyone here know different?

EDIT: A little research tells me that they are essentially the same. If there is any difference, the 7.62 may be fired in the .308 chamber, but the .308 should not be fired in a 7.62 chamber. Exactly the opposite of the other debate.

For me this one is moot. The .308Win is so common, I can't ever see myself buying 7.62x51.

Your understanding is correct in the generalities of things. The good rule of thumb is to not shoot 5.56 in a .223 chambered rifle; however, if it is a .223 Wyld chamber, you can safely shoot both. Then there is the whole discussion of when the rifle chamber was bored in the tool's life cycle. Some chambers are going to be looser than others as tooling wears BUT unless you are willing to do a complete chamber tolerance check to see if it meets 5.56 spec, I would still not shoot 5.56 out of a .233 Remingtion chamber.

Info I get on the .38/7.62 debate is mixed. Some experts say it's not safe to shoot .308 in a 7.62 chamber and others say it is since the pressure differences are so minor.

As far as buying 7.62 over .308, it depends on what you want to do. 7.62 bulk is pretty cheap (relatively speaking) if you want to "plink" and save the brass to reload. If not, there are cheaper alternatives if you are going to just throw the spent casings out. However, if you want your shots to really count, one is better getting good .308 ammunition since there is significant performance differences, especially at longer ranges.

A couple of months ago I set out to find out *exactly* the difference between 5.56 and .223. I knew that .223 could go in 5.56 but not vice versa, but I wanted to know precisely why.

I have to say - for how much one can find written by bloggers and such on the internet on this topic - I was stunned at how little *definitive* information that was out there. The signal-to-noise ratio seems very low. Lots of people would say they're "essentially" the same. Well - that's not very specific.

I've concluded that 5.56 fired brass and .223 fired brass are equivalent. You can't find 5.56 reloading dies, for example.

Many talk about the chamber pressure differences, but even that has controversy in that the pressure measuring methods apparently are different between the two calibers. (The data standards organizations.....SAAMI and whatever the other one is - have different methods for measuring chamber pressure.)

The reloading manual I have does not have data for 5.56 per se. I understand you can find "Service Loads" or something to that effect for .223 in some manuals - which I believe are what people would call "hot .223" loads.

Published muzzle velocity for the two rounds shows that 5.56 is a little faster - 6-7%.

The significant difference seems to be the physical dimensions - leade(?) specifically.

I'm concluding the real danger of putting a 5.56 round in a .223 chambered gun is, especially if the gun happens to have a pretty short throat, then that 5.56 round might end up touching the lands..........and then you get abnormal pressure spikes...and that could cause a very bad day.

OR

Let me add to the confusion......

On CZ USA's website ......FAQ

Q: Can CZ rifles chambered in .223 fire 5.56 ammunition safely?

Answer: "All of our .223s will happily eat 5.56. ....... we build everything to CIP spec, which doesn't differentiate between the two cartridges and just has the higher pressure as its standard..........."

otisrush said:

Many talk about the chamber pressure differences, but even that has controversy in that the pressure measuring methods apparently are different between the two calibers. (The data standards organizations.....SAAMI and whatever the other one is - have different methods for measuring chamber pressure.)

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Yeah, these two methods are different.

SAAMI uses a method that involves drilling a hole in the cartridge to install a pressure sensor. The EPVAT method requires the sensor to be placed just in front of the casing. This reduces error because no hole is drilled, but it does result in higher pressure numbers.

I don't know of any examples of a .223 chamber rupturing because a 5.56 round was fired in it. Still, the pressures are higher. The question is, how much higher?

I would love to do my own testing, but I just don't have the money for this.

otisrush said:

A couple of months ago I set out to find out *exactly* the difference between 5.56 and .223. I knew that .223 could go in 5.56 but not vice versa, but I wanted to know precisely why.

I have to say - for how much one can find written by bloggers and such on the internet on this topic - I was stunned at how little *definitive* information that was out there. The signal-to-noise ratio seems very low. Lots of people would say they're "essentially" the same. Well - that's not very specific.

I've concluded that 5.56 fired brass and .223 fired brass are equivalent. You can't find 5.56 reloading dies, for example.

Many talk about the chamber pressure differences, but even that has controversy in that the pressure measuring methods apparently are different between the two calibers. (The data standards organizations.....SAAMI and whatever the other one is - have different methods for measuring chamber pressure.)

The reloading manual I have does not have data for 5.56 per se. I understand you can find "Service Loads" or something to that effect for .223 in some manuals - which I believe are what people would call "hot .223" loads.

Published muzzle velocity for the two rounds shows that 5.56 is a little faster - 6-7%.

The significant difference seems to be the physical dimensions - leade(?) specifically.

I'm concluding the real danger of putting a 5.56 round in a .223 chambered gun is, especially if the gun happens to have a pretty short throat, then that 5.56 round might end up touching the lands..........and then you get abnormal pressure spikes...and that could cause a very bad day.

OR

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The leade seems to be the biggest difference between the two, so your conclusion may be why 5.56 in a .223 is no recommended.

As far as reloading, those that I know who reload will use either brass and load them to .223 specs. Some sort the brass by original cartridge type and load the powder differently since 5.56 cases tend to be thicker in the case wall and the base, so there is less room for powder.

My Hornady manual 9th edition only takes 223 Rem up to 55gr bullets then it goes to 223 Rem Service Rifle or 5.56 Nato for 68gr and up. My rifle is chambered for 5.56 so I just use the 5.56 data for my 69gr Match Kings. Don

5.56 in a 223 chambers can result in higher pressures, stuck cases, or sticky extraction in some guns.

It is not recommended, but like the 38spl vs +P debates the world is not going to implode if it happens. A lot of folks with bolt action rifles use them interchangeably despite not being specifically chambered for it.

In a semi automatic there's hardly a rifle out there anymore that isn't either a 5.56 or hybrid chamber.

One fellow was buying a new Mini-14 the other day, asking everyone if he could shoot 5.56. I told him I had one for years, and yeah, it's fine. He kept going on about it until I said, "Look, man, it's on the rifle and even on the box. I think you're good!"

Much ado...

On .308 the commercial ammo is usually higher pressure, though both are fine for either, save for some odd surplus rifles with long chambers.

Much good info here, and correct that the leade and pressure are the major differences. Now, let me tell you that several years ago I became your "crash test dummy". I had a Remington (I believe the model was the SPS Tactical) in .223. I had a bunch of ammo from an AR I had sold, and since the ammo was the same , I figured I'd shoot it up. Fast forward, I didn't blow the rifle up (good thing), I had some difficulty closing the bolt which became quite annoying (which I attributed to a problem addressed by Remington concerning improperly cut chambers). Needless to say I opted to just get rid of the rifle. It wasn't until later that I realized the difference in the leade length created my problem. I learned a lot from that.

In short, your sales guys are parrots, just repeating bad information to the detriment of their customers.

Thanks for the story gunny. I appreciate you allowing us to learn from your experience.

gunny4053 said:

In short, your sales guys are parrots, just repeating bad information to the detriment of their customers.

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Yeah, and I wish it weren't true.

This particular store does a very brisk business. They have no trouble selling everything they have. On their sale days, they have to have a separate room set aside just to do the paperwork on gun sales because there are so many people buying guns.

So, there's no need to try to "up-sell" at this store. I'm sure the salesman in this story was just beating his chest and trying to show how "knowledgeable" he was about stuff. Man, I hate that. All it does is confuse new buyers and, in this case, potentially cause harm to equipment or personnel.