Not recommended, unless the manufacturer of your specific make/model of your rifle claims/advertises that it is safe…

Lately there have been a lot of articles/youtube posts about this subject. Not sure if this question has already been posted here.

As I am no ballistic expert by any stretch, I do try to stay informed.

I just wanted to shed some light on this debate, so please don’t ‘shoot’ the messenger here (me) lol…

My primary concern was regarding my expensive investment, my Remington 700 .223, and that is why I did a some research on this subject.

When I first started shooting 223 rifles years ago, many gun stores/ranges would often (and still do today) hand me a box of 556 when I ask for 223. I have learned that these two calibers are very similar in casing diameter. However, 556 casings are loaded to higher pressures than commercial 223 casings. The 556 load requires military/law enforcement higher grain pressure specs, and often have slightly thicker case wall lining, which often can over-stress the 223 barrel/chamber.
So, can you shoot 5.56 in a 223 rifle?

Short answer: yes, but not recommended, according to many experts.

In addition to potentially damaging your 223 barrel/chamber, there also exists a potential danger to the shooter. Yea, I’ve shot 556 for years in my 223 rifles without any issues, but I certainly do not these days, just to be on the safe side.

Bottom line according to many experts it seems, if you have a .223 Rem. rifle of any type, it is not recommended that you use 5.56x45 mm ammunition, unless the specific gun manufacture states/advertises that it is safe. The general consensus seems to be, that you can however, safely shoot 223 Rem in a 556 rifle.

Lots of good reads online and youtube videos about this, so please check them out for yourself to form your own opinion, by searching for “223 vs 556”.

For you reloaders, you guys probably are already much more informed about this subject, so this posting is more for the casual weekend 223 shooter.

I hope this post helps some of you folks, thanks for reading and good shooting!

Thanks for the info...

Your correct. The 5.56 is not a safe bet in a .223 chamber for the reasons you stated above, plus the bullet on a NATO round will set dangerously close to the lands and grooves in a .223 chamber. This is another cause for an overpressure situation in a .223 chamber.

The 7.62 x 51mm NATO round is perfectly safe in a .308 Winchester chamber. Actually, the NATO round runs with a lower chamber pressure than the .308 as well.

Too bad it does not work the same way with the .223/5.56 ammo. I suppose that is the motivation behind certain gun makers coming up with bolt guns with 5.56 chambers.

Great info about the 7.62 vs .308. Thanks guys!

Very informative and helpful thanks for sharing.

Best rule of thumb is:
Civilian guns use civilian ammunition.
Military guns use military ammunition.
There again, as stated by the gun manufacturer, there are exclusions to the rule. Be safe and do your homework before substituting ammunition types.
The .357 Magnum wheel-guns are the only ones I know of that give the 'open' option to use .38 SPL and .38 SPL +P in those chambers. Again, research reliable resources before firing that assumed substitute!!!

I shoot 223 Winchester super x hunting rounds through an m4 variant I own and no problem I actually found the those rounds leave my system cleaner than using the mil grade 5.56 but like you guys mentioned above no 5.56 in a 223 only system the pressures from the cartridge are too high. But thats what makes part of the price difference as well. As far as using 223 hunting vs mil spec 5.56 I've much rather use the hunting varients for self defense scenario due to the ballistic testing between the two. Sure can get a much greater distance with the 5.56 but most engagement occurs within 200 yards.

I'm not so informed about the .223 vs. 5.56 specifics, but if it follows the .308 vs. 7.62 NATO, the following could hold true.
In the .308/7.62 NATO round substitution, it's not so much about pressure as it is about head-spacing.
The pressure specs originated from different testing technologies. The 7.62X51 NATO test was originally determined by CUP (copper-under-pressure) method (TMs, Army Ammunition Data). The .308's original numbers came by the use of Piezoelectric Sensors in the test chamber instead of copper plugs. There is no reliable conversion for the values from CUP to PSI methods other than the fact that when the pressure increases, their readings both go up.
Example: 7.62X51/.308 measures 50,000 TM PSI; 52,000 SAAMI CUP; & 62,000 SAAMI PSI
5.56X45/.223 measures 55,000; 52,000; 55,000 respectively
.30-06 measures 50,000; 50,000; 60,000 respectively, and last,
.30 Carbine measures 40,000; 40,000; 40,000... lateral across the methods. Go figure!?
ABOUT HEADSPACING:
GO: .308=1.6300; 7.62=1.6355
NO-GO: .308=1.6340; 7.62=1.6405
Field Reject: .308=1.6380; 7.62=1.6455
I don't think I'd want to rattle something down my barrel that doesn't fit the chamber correctly, nor would I want a bunch of bore-hugging 7.62s marring my .308's action, or worse, damaging the barrel and/or injuring someone standing by.
My advice... Stick with ammunition recommended by your gun's manufacturer.

Good info exchange gentlemen...

My AR is chambered for 5.56x45mm, so that is usually what I shoot.

There is some good accurate information being put out here in this thread, and there is some poor/incorrect info leaking in (not much, but some) as well.

But overall I think the overall quality of the info is fairly good.

Rick 51/ R51 wrote:I'm not so informed about the .223 vs. 5.56 specifics, but if it follows the .308 vs. 7.62 NATO, the following could hold true.
In the .308/7.62 NATO round substitution, it's not so much about pressure as it is about head-spacing.
The pressure specs originated from different testing technologies. The 7.62X51 NATO test was originally determined by CUP (copper-under-pressure) method (TMs, Army Ammunition Data). The .308's original numbers came by the use of Piezoelectric Sensors in the test chamber instead of copper plugs. There is no reliable conversion for the values from CUP to PSI methods other than the fact that when the pressure increases, their readings both go up.
Example: 7.62X51/.308 measures 50,000 TM PSI; 52,000 SAAMI CUP; & 62,000 SAAMI PSI
5.56X45/.223 measures 55,000; 52,000; 55,000 respectively
.30-06 measures 50,000; 50,000; 60,000 respectively, and last,
.30 Carbine measures 40,000; 40,000; 40,000... lateral across the methods. Go figure!?
ABOUT HEADSPACING:
GO: .308=1.6300; 7.62=1.6355
NO-GO: .308=1.6340; 7.62=1.6405
Field Reject: .308=1.6380; 7.62=1.6455
I don't think I'd want to rattle something down my barrel that doesn't fit the chamber correctly, nor would I want a bunch of bore-hugging 7.62s marring my .308's action, or worse, damaging the barrel and/or injuring someone standing by.
My advice... Stick with ammunition recommended by your gun's manufacturer.

I fully agree with this and would only shoot ammo that is designated for any of my guns. I also agree with the .308/7.62 stuff as well. Besides, most military surplus ammo that I have shot (except for 7.62 x 54r), is not as well made or as accurate as civilian manufacture. Oddly, I have bought Winchester 7.62 x 54r and found that it is not nearly as accurate as ComBloc surplus...even in similar bullet weights. Guess my Russian guns only want fed "Warsaw Pact" fodder!

I have to say that the civilian ammunition is quite reliable once you find the balance between what each of your firearms ingest reliably, and which brands line up with the results you're after. Not to forget that some compromise comes into play when a good shooting ammo is awfully dirty. My S&W 22A-1 pistol loves Eley and Remington but fails miserably with Federal Champion and a few others. I picked up a 500 brick of Norma from Midway and I'm anxious to see if it is as clean and accurate as I remember Norma to be. Most of the rest of all my rifles and pistols do best with varied Remington ammunition, but always bulk Remington UMC 45 ACP 230 grain FMJ, 9mm 115 grain FMJ, and 9mm+P 124 grain FMJ (all round nose) for the range. My Colt is a tack-driver with it. Then, for my Winchester Model 88 .308, I hunt with Remington Core-Lokt 150 grain PSP and target work gets Federal Gold Medal Sierra Match King HPBT in 168 grain. My S&W 520 NYSP (1980 only) N-Frame will shoot anything, but I stick with Remington for .38 SPL+P & .357 Mag and Hornady for .357 Mag for precision target shooting. I used to reload my own back in the day, but the premium civilian ammunition these days has come to be a stable balance of reliability with almost un-noticeable variance in performance and results on the target. I don't even look for the same LOT numbers on the packages any more. And, I don't buy ammo by finding the lowest cost per round. The headache isn't worth the savings to me.
Surprisingly enough, the Blazer Brass is just as clean and reliable as the UMC, although, groups aren't as consistently tight as with UMC. A 1-1/2" group at 15 yds with UMC quickly turns into 2-3/4" groups with an occasional 3"+ stray.

Good to know, thanks for the info!

Rick 51/R51. I have to pass this on to you. When I still had my .22 LR chambered rifle, I had used all sorts of ammo manufactures...as we all have. There is one brand I had bought a brick of, and it was the best shooting "cheaper" brand I had ever used. It was made by Centurion I believe. It burnt really clean, and had a good smell that is similar to the Eley stuff. It was very accurate and was half the cost of the Eley...it was HV though, not standard. The day I came across this stuff was at the very start of the .22 drought, and I should have been smart enough to buy more than one brick. Just wanted to pass this on, and I highly recommend that .22 ammo.

Sorry that it was a little "off topic", but I had read your post above, and wanted to pass that on to you or anyone who is still shooting .22.

I believe Centurion .22 LR is made in Mexico, but also that it's pretty reliable, clean, and has a good bullet-to-case fit. Pretty accurate too, especially for the price. I'd buy some to try in my finicky guns that like larger rim diameters. Just haven't run across any.