Firing 5.56 out of an M&P15I

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pierrody

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I have a Smith & Wesson M&P15I (heavy barrel) that says "223 REM" on the barrel.

Can I fire 5.56 ammo in this rifle? I have heard conflicting things from different people and would like a definitive answer.
 
Yes, considering the restriction on exportation of 5.56 by the US States department, if you can get your hands on some,you can use it, but I wouldn't use it exclusively the excessive pressure will cause premature wear and eventually failure.
 
I will have to say no on that.
The 5.56mm cartridge operates on higher chamber pressures that the .223 rem. A 5.56 will chamber in a .223 but its not safe. A 5.56 chamber has a longer throat to deal with the hinger pressures. A 5.56 case has a thicker base than the .223 to also help with the higher pressures.

Its not something I would do to my rifle after I spent a large chunk of change on it.
 
Someone had mentioned that the "223 REM" stamp on the barrel may just be something S&W put on the rifle to get around State Department export restrictions and the chamber is actually 5.56.
 
CommonLawyer said:
Someone had mentioned that the "223 REM" stamp on the barrel may just be something S&W put on the rifle to get around State Department export restrictions and the chamber is actually 5.56.
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I would tend to believe this, considering the rifle is a "Military and Police" model to begin with.
 
am I the only one who thinks that spelling and grammar mistakes in a reply discredit the author? It's hard to take someone seriously when they can't handle the simple task of manipulating the english language.
 
Wally said:
am I the only one who thinks that spelling and grammar mistakes in a reply discredit the author? It's hard to take someone seriously when they can't handle the simple task of manipulating the english language.
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This train is now headed to OT. Extra fare required.
 
hbean said:
Yes, considering the restriction on exportation of 5.56 by the US States department, if you can get your hands on some,you can use it, but I wouldn't use it exclusively the excessive pressure will cause premature wear and eventually failure.
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Scharfschütze said:
I will have to say no on that.
The 5.56mm cartridge operates on higher chamber pressures that the .223 rem. A 5.56 will chamber in a .223 but its not safe. A 5.56 chamber has a longer throat to deal with the hinger pressures. A 5.56 case has a thicker base than the .223 to also help with the higher pressures.

Its not something I would do to my rifle after I spent a large chunk of change on it.
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Check your facts, both of you. It will not cause premature wear and no it is not unsafe. Dimensionally the catridges vary but its not a safety concern. Carry on...:rolleyes:

TDC
 
I really don't think you have anything to worry about...friends and I have shot 5.56 and .223 interchangeably in various rifles over the years without any problems. Also, if I recall correctly, my Lee and Barnes loading manuals, as well as data I downloaded from Loaddata don't make any distinction between the two.
 
Differences

Everything I have read in regards to this topic, states that there is no difference between the two in regards to measurements. BUT there is a huge difference in the pressures generated. The 5.56 is supposed to produce more pressure than the .223. Not that it is a big deal, as I have not seen 5.56 for years now.
 
CommonLawyer said:
Someone had mentioned that the "223 REM" stamp on the barrel may just be something S&W put on the rifle to get around State Department export restrictions and the chamber is actually 5.56.
Click to expand...
Perhaps with a small manufacturer, this might be true - but I doubt Smith & Wesson is going to jeopardize thier US government contracts over thier tiny (comparative) export business.
 
Other M&P15 models sold in the US are stamped 5.56. I have the same M&P15I as you, stamped .223 and wouldn't hesitate firing 5.56 with it. The "I" model is for states with stricter regs. There is no way the S&W would make an entirely different set of tools, dies etc to get by export regs for such a small market. The added cost to make a different barrel which is almost identical would make no sense. To make a different barrel stamp cost a couple bucks and solves the problem.
 
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