I had been looking at an Olympic Arms AR but started talking today with someone regarding the S&W M&P-15. I'm not familiar with this rifle at all. Can it fire the 5.56 or is it strictly .223?

M&P 15s are chambered for 5.56 NATO, so they can safely fire either 5.56 or 223 Remington ammunition.

The M&P is a much better rifle, the price on the Olympic Arms may sound better, But you get what you pay for. I know a couple who regreted there Olympic Arms purchase. Go with the 5.56 NATO so you can shoot either.

I really like the M&P and would unquestionably choose it over the Olympic (although to be fair a lot of people like the Olympics). The big question for me was, could the M&P fire the 5.56. I can get ball ammo for about half of what I'd pay for .223. I just went to the S&W site and looked at the owners manual for the MP-15 and there it said .223 only!!

Well I just went back to the S&W site. In their description it does say 5.56 NATO. For some reason though the owners manual warns agains using it and says the barrel is stamped .223.

This is what the manual says:

http://www.smith-wesson.com/wcsstore...10-10-2010.pdf page 9

M&P 15s are chambered for and marked 5.56 NATO, so you can shoot either 5.56 or 223.

My M&P 15PS says 5.56 on the barrel.........I'm sure they are all the same, except for the .22LR.

Excellent. Not having one here to check I wasn't sure. Much as I like the Smith, .223 only would have been a deal breaker.

My Sport barrel is marked 5.56 as well as 1/8 and 5R which I assume designates the rifling.

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JT

My M&P MOE is stamped 5.56 as well

Come on guys, lets not have a million posts about "my barrel is marked....". The M&P 15 is chambered for 5.56, end of subject. Stop worrying about this, forget the Olympic Arms, and buy an M&P 15 if that's what you want.

I wonder why S&W puts that warning in their manual. Do they make an AR chambered in .223?

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JT

Woah settle down... just trying to be helpful guy.

I am REALLY glad all you guys posted what was stamped on your barrel. I just got my M&P today and for a moment thought there was a problem. Seeing that you guys had the same thing stamped on yours as I have on mine did the trick for me.

THX !!

There are some barrels made that are chambered for .223 and you sometimes find them on less expensive rifles. You might be able to shoot 5.56 out of it but you are risking yourself and anyone around you when you do it. Generally bolt actions are chambered for .223 and the semi's are chambered for 5.56, but as I said before some of the really cheaply made rifles will cut corners by using a barrel and extension for .223 and not .223 wylde. S&W M&P15's are 5.56 the 1-8 is one twist in 8 inches of barrel length and the 5R is a style of rifling normally found in high end hunting rifles like Remingtons new high end rifles.

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Grover Oathkeeper

#4 posting........My SPORT barrel is stamped 556 NATO also. Sorry Dragon88, just messing with you.

If is says 556 NATO you can shoot both 556 and .223. If it says .223, stick to .223 unless you want to risk injury.

The only difference between the .223 and 5.56 is when the .223 first came out it was designed for lighter bullets and these rifles had a shorter throat. I have a newer .223 bolt action rifle with a long throat and a 1 in 9 twist and can shoot both types of ammunition.

If you have an older .223 rifle with a short throat shooting 5.56 NATO ammunition can cause pressure spikes due to its shorter throat.

The European CIP, the equivalent of the American SAAMI considers the .223 and 5.56 NATO to be the same cartridge rated at the same approximate chamber pressure.

NOTE: The SAAMI measures chamber pressure at the mid point of the cartridge case. And the NATO standard for measuring chamber pressure is at the mouth of the case which reads higher than SAAMI testing standards. If SAAMI testing standards were used on NATO 5.56 ammunition the pressures would be approximately the same.

Live in Ontario Canada bought M&P15 i model #811010 its stamped 223 on barrel,owners manual says 223 only,rifle guys say yes shoots both,some say no at club ? although it makes no difference to me if capable of shooting both types of ammo my training says 223 only, iam i correct,USA have diff laws!also mine has no flash sup is it worth it to put one on how much should it cost to mill barrel!?? thanks Canuck jpmp15!

canadian laws require a different set of marking systems, something about military ammo. As far as I can discern the barrel you got up there is the same barrel and chamber sold down here. It is just marked different for export to Canada! happy shooting. Does it say 1:8 5R or not. If not what does it say? I have found running them with and without muzzle attachements, I honestly find that without one the rifle seems quieter, any muzzle attachement will change the way the rifle shoots and after you add one you will have to resight it in. Personally I prefer to not have them but the model I bought has one and I changed it out to one that affects the accuracy less than the A2. I was able to test them side by side. Its your call, if you have it done find a good competent smith and make sure he gets it indexed correctly. I looked it up and it has a 17" barrel with a chrome lining. It says .223 only but I think that is a legality, it doesnt have the cutout for the grenade launcher, Colt on their export models chambered theirs for 222rem but S&W stayed with .223. I myself would shoot it and take a fireformed case and measure it. You should be able to get the specs for a .223 chamber and a 5.56 chamber and see what the specs on your fireformed case come up to be. You can also measure your chamber length to help find out. It really is a good looking rifle and I dont understand why it has been discontinued other than some silly legal issue. Personal belief is that it will shoot both just fine, but that is just my opinion and if I had it I would shoot 5.56 in it or my reloads which are supposedly .223 but loaded to service rifle standards.

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Grover Oathkeeper

I love the Rifle its amazing and accurate thanks for the info on specs,i will look later and post what is says about model 811010 is a blank on sw site says discontinued!

only markings on barrel is .223 1/9 ?

I will bet it is a cut down 18" barrel or 20" with the standard chrome lining and the 1:9 twist. Most of their rifles used to have the 1:9 twist until they found out what a score the Sport barrel is, they have since started changing some of them over. A 17" barrel is an odd duck but you are concerned with the chamber size. everything else would pretty well be standard.

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Grover Oathkeeper

thanks for input on 223 and flash info think i will leave stock!happy shooting from Canada!