.223 vs .556

[Bizkitjmd1]

I know this has probably been discussed before so maybe someone can point me in the right direction.

Just picked up a S&W M&P15I last Saturday and it is stamped .223. Now the guy at the store and a range master on Sunday told me I can put .556 through it no problem. I know .556 is a hotter round, but is there any possible risk of running .556 through a .223 rifle?

 

[bpm990d]

A brand new rifle and chamber, it will have significantly increased pressures if it is a SAAMI .223 chamber. It is on the SAAMI Unsafe Arms & Ammo combination list.

However there are a number of .223 chambers that should be good to go with, for instance the .223 Wylde chamber is ok with 5.56mm. You need to find out what .223 chamber they put in it. Maybe someone will chime in.

B

 

[Supermoto]

what is interesting is that every other S&W AR is marker 5.56/.223 or 5.56, but your is the only one marked .223

I would call S&W to find out why

 

[mr_hao]

I believe the rule of thumb is any rifle marked 5.56 can fire .223 but not the other way around. ie a rifle marked .223 can not fire 5.56

 

[radioman]

If there's a big enough difference for some to consider dangerous, how come many of the ammo boxes I buy have both 5.56 and .223 marked on them?? Does this in-itself mean that these particular rounds are safe for both?

 

[AbbyOakley]

when in doubt RTFM....read the fabulous manual (to the gun)

 

[In God We Trust]

All this time I thought they were exactly the same round.

 

[meth0d]

Check it out:
http://www.northeastshooters.com/vbulletin/threads/30450-.223-vs.-5.56-explained

 

[Steve_P]

Does it say 223 on the receiver or on the barrel? I would bet that the barrel is marked 5.56

 

[uzz75]

Bizkitjmd1, did you try to check the chambre with go no-go gauge ?
i'd like to buy M&P15I but at this point i'd like to know the realy chamber.

Thanks
Michele Schiavo

 

[wahsben]

The way I remember which one is safe to shoot in the other is that 223 is a smaller number than 556 so smaller fits into larger but not vice versa. Although there are guns you could shoot 5.56 in a .223 it is not recommended.

 

[xtry51]

Per S&W's website, .223 ONLY. Do not run 5.56, it is not a wylde chamber

LINK

 

[drgrant]

That's really weird... why the hell would they make a rifle like that with a thin barrel that only takes .223 ? Unless it's a misprint, or something. If that's true, it's probably one of the only carbine type AR style rifles like that on the market.

-Mike

 

[Blitz1]

 

[uzz75]

I now about 223 vs 556 difference , CUP and SAAMI pressure.
I just like to know if the 15I model is a real 223 o 556.
The 15I model is the only model avaiable for the end-user.
BushMaster also is 223 write for the end-user but is realy 556 if checked with go no-go

Thanks.

Michele

 

[meth0d]

I now about 223 vs 556 difference , CUP and SAAMI pressure.
I just like to know if the 15I model is a real 223 o 556.
The 15I model is the only model avaiable for the end-user.
BushMaster also is 223 write for the end-user but is realy 556 if checked with go no-go

Thanks.

Michele

I'm not sure what you mean about it being "the only model available for the end user", but the 15I is the only one (with the exception of the 15R that is 5.45x39mm) listed on S&W's site that specifically says ".223 Only"; so since they build the rifles, and are responsible for their website, I think it's safe to say that the 15I is .223 only.

If that's not good enough to satisfy your inquiry, you can always contact them directly: At this Link

 

[mac1911]

going out on a limb here but Im thinking both 5.56/.223 gonogo gauges will work
I am no expert but belive the NATO 5.56 besides built to take the added preasure of the 5.56 Nato round is a little on the loose side compared to a .223 chamber.
Maybe this model is geared more twards hunters or maybe where MILITARY SPEC ammo can not be sold ?????????

In The End My dad would say. If it dont say it, it aint. right from S&W web site it states .223 only

Now if your 5.56 ammo is not labeled loaded to NATO specs or military specs , IS IT really 5.56 ?

just for example WOLF now puts out a brass cased M193 5.56 loaded to US military specs, now is the US military specs different than NATO specs ???? more questions.

I would do as manufacture says. .223 only so no m193 or m855 loadings for that gun

also foresters products is the only manufacture that I have come acrosss that has a NATO specific head space gauge

http://www.fulton-armory.com/556-vs-223-Chambers.htm here is a good read

 

[bpm990d]

The 5.56mm and .223 headspace gauges are a little different. The problem arises, when the gun is fired. Headspace tends to grow and after a while a formerly .223 chamber that wont take a NOGO SAAMI gauge will now swallow a Military NOGO. Also headspace gauges do not tell you anything about the throat of the rifle. In my opinion when talking about pressure, the more important dimensions are the throat.

The .223 chamber has a little more than half the freebore of a 5.56mm chamber. In a brand new .223 chamber, the bullet is right next to the rifling and has almost no jump. Very good for accuracy, but very bad for dealing with cartridges that are designed to be shot in chambers that have lots of jump (5.56MM). Getting close to the rifling tends to raise pressures dramatically.

If you fire a couple thousand .223 rounds out of a .223 chamber it's no longer going to be a .223 chamber. The throat is going to be washed away and it will be closer to a 5.56mm throat. You can use a tool like a Hornady Lock-N-Load gauge to measure how far the throat has moved forward. Any High Power shooter will tell you that is the reason they replace their barrels every year or every other year is that the throats are gone after several thousand rounds.

ar15barrels.com has an excellent tech. page.

B