Quote:
Originally Posted by MikeRizz
I am considering purchasing a M&P 15, but am a bit confused by all the different models, 15T, 15Sport, 15PS, etc. I really like the 15MOE in flat dark earth color. Is there a preference between 223 or 556 ( I thought they were basically the same round )? Any help appreciated! I am AR newb. I have looked at all of them of the SW website just not sure which accessories are worth buying.
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If memory serves me correctly, and I have not gone back to check, basically, its a difference between the SAAMI and NATO standards for .223 vs 5.56. There are two standards: SAAMI (Sporting Arms and Ammunition Manufacturers' Institute) and NATO
5.56 chambering (NATO mil-spec chambers) have a longer lead, which is the distance between the mouth of the cartridge and the point at which the rifling engages the bullet. The .223 chambering ("SAAMI chamber") has a shorter lead. The 5.56 has a higher pressure than the .223. I think the confusion between the use of 5.56 in a .223 only weapon arises from the fact that the .556 Nato round uses, as its parent case, the case of the .223, and that some of the .223 history involves the .223 Remington being standardized as the 5.56x45mm for the M-16 in the early 60's but people don't realize that when it was introduced as a sport round later that it was actually a little different and used a different standard for sport use manufacturing.
Using commercial .223 in a 5.56 chambered rifle should work reliably, but generally will be a little less accurate due to the excessive (5.56) lead. Using 5.56 in a .223-chambered rifle can cause excessive wear and stress on the rifle and even be unsafe (the SAAMI standard recommends against the practice).
If the rifle is marked for 5.56 then you can use .223, but if its marked for .223 only then its really not a good idea (in my opinion, and that of SAMMI) to use 5.56. Although, some people do get away with it as some commercial rifles marked as ".223 Remington" are suited for 5.56.
If you use 5.56 in a .223 only rifle, you should consult the manufacturer first before doing such. Some signs that the 5.56 might not be acceptable for that .223 only rifle, aside from a weapon malfunction (if your lucky in some cases), or possible injury as a result, is excessive pressure signs such as flattening or gas staining of the primers.
A weapon is like any tool, if you use it within its intended specifications then it works for its intended use. One of the primary gun safety rules is to always use the correct ammunition for the weapon.
Here is one brief reference, there are many more via Google:
http://fulton-armory.com/faqs/AR-FAQ...3-Chambers.htm
Here is the SAMMI site as well:
http://www.saami.org/specifications_...tion/index.cfm > where in the "Unsafe Firearm - Ammunition combination" standards (
http://www.saami.org/specifications_...mbinations.pdf ) On page 7, it states:
In Firearms Chambered For:
.223 Remington
Do Not Use These Cartridges:
5.56mm Military
222 Remington
30 Carbine
(The "5.56mm Military" is the 5.56 Nato)
So it comes down to this:
If its chambered for 5.56 you can also use .223
If its chambered for .223 only then do not use 5.56
There are some marked .223/5.56, these are generally actually chambered for 5.56 but the .223 will work. However, I personally only look for marked as 5.56 chambered and don't pay attention to the ".223/5.56" marked rifles because some of these places may have marked for "advertising" purposes (but are probably correct in their marking as to use of the .223 in the weapon) and although thats not bad I just feel more comfortable knowing what the weapon was built for exactly and besides a single specific chamber designation is required for my use. However, I think the real reason some are dual marked as .223/5.56 is for legal reasons.
If I scewed this up I apologize, going from memory here as it never concerns me as I use the round the weapon is actually chambered for which in my case is 5.56.