I'm eventuall going to buy a Smith 223. The one that seems to have the most appeal to me is the M&P 15 TS. The other is the Sport, simply because it is so inexpensive. Of all the 223's Smith makes which would you recommend and why?

Not to be a nit picker but actually I believe all the M&P's are chambered in 5.56 specifically. I know they are almost the same but I feel it's important to make the distinction.

That being said, personally I believe the Sport is the best value out there right now for shooting either .223 or 5.56. You can keep it as a sporting rifle or take it the tactical route and it works great for just about any application.

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This Signature is too Short!

OK. What is the difference between 223 and 5.56?

Answer can be found here

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M&P9/9C/Shieldx2/Sportx2/15-22

I'm something of a novice on the subject so I'll let others take that question but from what I understand, the neck is slightly different and obviously 5.56 normally packs a bit of a bigger punch, my 5.56 is 62 grains and my all my .223 I've found is 55 grain, not to mention it's also harder to get (the 5.56 that is). I was also told by my LGS owner that .223 would wear on my barrel more than 5.56, however I'm somewhat skeptical of that comment.

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5.56 generates higher pressure and the brass case is a bit thicker. It requires a slightly longer chamber to handle the increase pressures developed.

Some S&W ARs ARE chambered for .223 but those are the custom shop type offerings with longer bbl.s intended for match shooting.

The "T" model would be my choice of the two you mentioned but everyone has different opinions and priorities. If you are going to accessorize the Sport, the price difference becomes less of a gap.

I have the "optics ready" model. It has the forward assist and dust cover, but no iron sights. No biggie for me as I run an optic and prefer Magpul BUIS. I got this rifle in a trade or I too would have bought the Sport model.

I have a thousand rounds of 55gr federal 5.56x45 that doesnt say .223 on it, you can get either load in basically whatever bullet weight that you want. I am not sure about .223 but 5.56 actually takes a .224 bullet plus the throat length and angle of the shoulder are different. If the rifle is chambered for .223 and doesnt say 5.56 on it anywhere SAAMI recommends you not shoot 5.56 in it because of the chamber pressure difference. In a .223 exclusive rifle everytime you pull the trigger on a 5.56 you are running a chamber test proof round through it which can lead to catastrophic failure. .223 ammo is Made to Saami spec which the top chamber pressure is 50,000cup while 5.56 is made to Nato Spec and the chamber pressure is 70,000cup. There is a lot of info to be found and read on this subject. enjoy.

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Grover Oathkeeper

5.56 mm NATO versus .223 Remington

The 5.56 mm NATO and .223 Remington cartridges and chamberings are similar but not identical. Military 5.56×45mm cases are often made thicker and therefore have less case capacity.[17] However, the NATO specification allows a higher chamber pressure. NATO EPVAT test barrels made for 5.56 mm NATO measure chamber pressure at the case mouth, as opposed to the location used by the United States civil standards organization SAAMI. The piezoelectric sensors or transducers NATO and SAAMI use to conduct the actual pressure measurements also differ. This difference in measurement method accounts for upwards of 20,000 psi (140 MPa) difference in pressure measurements. This means the NATO EPVAT maximum service pressure of 430 MPa (62,000 psi) for 5.56 mm NATO, is reduced by SAAMI to 55,000 psi (380 MPa) for .223 Remington.[18] In contrast to SAAMI, the other main civil standards organization C.I.P. defines the maximum service and proof test pressures of the .223 Remington cartridge equal to the 5.56 mm NATO.

The 5.56 mm NATO chambering, known as a NATO or mil-spec chamber, has a longer leade, which is the distance between the mouth of the cartridge and the point at which the rifling engages the bullet. The .223 Remington chambering, known as SAAMI chamber, is allowed to have a shorter leade, and is only required to be proof tested to the lower SAAMI chamber pressure. To address these issues, various proprietary chambers exist, such as the Wylde chamber (Rock River Arms)[19] or the ArmaLite chamber, which are designed to handle both 5.56 mm NATO and .223 Remington equally well. The dimensions and leade of the .223 Remington minimum C.I.P. chamber also differ from the 5.56 mm NATO chamber specification.

Using commercial .223 Remington cartridges in a 5.56 mm NATO chambered rifle should work reliably, but generally will not be as accurate as when fired from a .223 Remington chambered gun due to the longer leade.[20] Using 5.56 mm NATO mil-spec cartridges (such as the M855) in a .223 Remington chambered rifle can lead to excessive wear and stress on the rifle and even be unsafe, and SAAMI recommends against the practice.[21][22] Some commercial rifles marked as ".223 Remington" are in fact suited for 5.56 mm NATO, such as many commercial AR-15 variants and the Ruger Mini-14 (marked ".223 cal"), but the manufacturer should always be consulted to verify that this is acceptable before attempting it, and signs of excessive pressure (such as flattening or gas staining of the primers) should be looked for in the initial testing with 5.56 mm NATO ammunition.[23]

It should also be noted that the upper receiver (to which the barrel with its chamber are attached) and the lower receiver are entirely separate parts in AR-15 style rifles. If the lower receiver has either .223 or 5.56 stamped on it, it does not guarantee the upper assembly is rated for the same caliber, because the upper and the lower receiver in the same rifle can, and frequently do, come from different manufacturers – particularly with rifles sold to civilians or second-hand rifles.

In more practical terms, as of 2010 most AR-15 parts suppliers engineer their complete upper assemblies (not to be confused with stripped uppers where the barrel is not included) to support both calibers in order to protect their customers from injuries and to protect their businesses from resultant litigation.

taken from wikipedia search 5.56vs.223

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Grover Oathkeeper