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Discussion Starter #1
Hi everyone i picked up my first AR which is a S&W M&P 15 sport chambered in 5.56 NATO, and i also bought .223 rem and shoot about 35 rounds not much. my question is can i use .223 rem in it. the only i ask after i fired them through is because i didn't notice it was only chambered for 5.56. freaking out a bit
 

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Don't worry you are safe! My barrel is 5.56 and i haven't even shot 5.56 ammo but had shot more than 1k rounds of .223
 

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Standard .223 can only shoot .223.
5.56 can shoot either 5.56 with normal or 2.23 with slightly reduced accuracy.
.223 Wylde can shoot either .223 or 5.56 with match grade accuracy.
 

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The 5.56 has thicker case walls, meaning reduced powder capacity, the 5.56 has a shorter throat than a .223 chamber. A .223 is pressure tested SAAMI style in the middle of the case, where pressure readings are highest. The 5.56 chamber pressure is measured from the case neck ( might be wrong but I think that is a military method) where the pressure measured is lower than the mid point, and the 5.56 is still measured higher than a .223. Put a 5.56 in a .223 chamber and you could get dangerously high pressures. Most guns will take it and you won't notice until some number of rounds later and the metals in your gun have had all the beating they can take. You might lose some accuracy one way or the other, but the concern is high chamber pressures.
 

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Shooting 223 in a 556 rifle will yield lower than normal chamber pressures and is safe. 556 in a 223 chamber will yield chamber pressures as great as 20k psi higher than normal. NOT SAFE

OP, you are safe. Just understand there will likely be a shift in zero should you start to shoot 556.

EDUB
 

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I just love to see these back and forths. One will show up on some Forum every day or so.

The .223 is a SAAMI specked chambering. The 5.56 is not, it meets the prevailing Military needs of the day. Pressures are measured in differing methods by both inanities.

In an extreme situation, run what ever you have that will fit. For day to day use, stick to what the barrel is marked. Will your weapon blow up? I wouldn't thinks so, but it will not be good for the weapon and could shorten it's usable life. Why risk it?

For me, I load everything I shoot. I have three standard .223/5.56 loadings.

First is a 55 grain bullet and is some what hot in a .223 chamber but usable (un-marked). It runs great in any and all ARs that I have tried.

The second is loaded for accuracy in my very tightly chambered .223 with a 1 in 14 twist. They are 50 grain bullets and make one hole at a hundred yards and are not even close to being hot in that bolt gun (tips are rolled on a red ink pad, bullet shapes are the same between the 50 and 55 grain).

The last is an equivalent loading with 55 grain bullets for my 20 inch AR with a Wyled chamber (rolled on a black ink pad).

All will function in all of my .223/5.56 weapons, just much better and safer in some.

You will do what you want but think about lengthening the usable life of your .223s and for that matter the lighter loads function a 5.56 chamber well and could add to the longevity there as well.
 

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Lets not forget that the gas port in a 223 is ,or should be, drilled for the lower pressures. So shooting 556 will result in an over gassed condition. Which is much harder on the bolt and the rest of the action.

EDUB
 

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Discussion Starter #15
oldpapps said:
I just love to see these back and forths. One will show up on some Forum every day or so.

The .223 is a SAAMI specked chambering. The 5.56 is not, it meets the prevailing Military needs of the day. Pressures are measured in differing methods by both inanities.

In an extreme situation, run what ever you have that will fit. For day to day use, stick to what the barrel is marked. Will your weapon blow up? I wouldn't thinks so, but it will not be good for the weapon and could shorten it's usable life. Why risk it?

For me, I load everything I shoot. I have three standard .223/5.56 loadings.

First is a 55 grain bullet and is some what hot in a .223 chamber but usable (un-marked). It runs great in any and all ARs that I have tried.

The second is loaded for accuracy in my very tightly chambered .223 with a 1 in 14 twist. They are 50 grain bullets and make one hole at a hundred yards and are not even close to being hot in that bolt gun (tips are rolled on a red ink pad, bullet shapes are the same between the 50 and 55 grain).

The last is an equivalent loading with 55 grain bullets for my 20 inch AR with a Wyled chamber (rolled on a black ink pad).

All will function in all of my .223/5.56 weapons, just much better and safer in some.

You will do what you want but think about lengthening the usable life of your .223s and for that matter the lighter loads function a 5.56 chamber well and could add to the longevity there as well.
So I shouldn't shoot 223 out of my 556 ?? This is confusing
 

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dabbson said:
So I shouldn't shoot 223 out of my 556 ?? This is confusing
It's okay. Just start by remembering this. If it's marked .223/5.56 or just 5.56 or multi you can safely shoot either. If it's marked .223 only shoot .223
 

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dabbson,

Sorry for the confusion. The .223 is not a problem in a weapon chambered in 5.56. I should have explained better.

The whole thing get very confused when we get into the differences in throating and other chambering variations. So we don't need to go there.

Think of it like shooting a 38 special in a 357 Mag chamber. Way back, there were revolvers that had cylinders that would accept the longer 357s. Think of that as running 5.56s in a .223 chamber, only your AR is much better built. The big difference is there is so little difference between the .233 and 5.56 outwardly. It still isn't a good idea for day to day use and most likely accelerate wear.
 

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Discussion Starter #19 (Edited)
oldpapps said:
dabbson,

Sorry for the confusion. The .223 is not a problem in a weapon chambered in 5.56. I should have explained better.

The whole thing get very confused when we get into the differences in throating and other chambering variations. So we don't need to go there.

Think of it like shooting a 38 special in a 357 Mag chamber. Way back, there were revolvers that had cylinders that would accept the longer 357s. Think of that as running 5.56s in a .223 chamber, only your AR is much better built. The big difference is there is so little difference between the .233 and 5.56 outwardly. It still isn't a good idea for day to day use and most likely accelerate wear.
If I shoot 223 it will accelerate wear on my 5.56 ? Please Lmk I really don't want to damage my new AR that would be sad
 

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Don't confuse yourself with the depth information, just keep in mind that you are safe and nothing to worry about.
 
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