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Old July 29, 2010, 05:56 PM   #1
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Colt Sp1 .223 or 5.56?

I am wanting to buy a Colt Sp1 retro Ar. My question is, can the Colt Sp1 fire 5.56 NATO rounds or is it .223 only? Correct me if I'm wrong, but I thought rifles like the Ruger Mini 14 which say .223 on the rifle can fire 5.56 as well. Is the Colt Sp1 the same? Or is it .223 only.
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Old July 30, 2010, 04:05 PM   #2
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5.56mm is the Army (NATO) designation for the ammo it is the same as .223 and will fire in any rifle so marked either 5.56 or .223 like the Mini 14's and AR15's.
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Old July 30, 2010, 04:10 PM   #3
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5.56mm is the Army (NATO) designation for the ammo it is the same as .223 and will fire in any rifle so marked either 5.56 or .223 like the Mini 14's and AR15's.
Incorrect....The 5.56mm is loaded hotter than the .223, so if you're AR-15 BARREL is NOT stamped for 5.56, you cannot shoot 5.56 through a .223 stamped barrel, unless you want pieces of 7075 alloy in your face.
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Old August 1, 2010, 06:42 AM   #4
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Wrong - a true Colt SP1 is 5.56, even if marked .223.

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Old August 1, 2010, 04:57 PM   #5
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My SP-1 shoots 5.56NATO all day long.

old Sneaky Pete here> I have shoot over 4000 rounds of "Issue" 5.56NATO 55gr FMJ thru my '73 Colt SP-1. I'd just go down to my Arms Room and have my armorer issue me 1000 rounds for "Tranging" purposes--I was on my Bn. Rifle Team. No questions--No problems. and this Horse Hockey about 5.56 NATO being "Hotter" --perhaps with "off the shelf" Wal-Mart ammo in .223Rem but my handloads for matches run 125>150 FPS faster than the 5.56 NATO stuff---more FPSs= more preasure! I personally do no know or heard of someone's rifle Blowing-up cuz he used a 5.56NATO in his .223Rem chamber???? THANX--SNEAKY
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Old August 1, 2010, 05:32 PM   #6
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The Difference Between 223 Rem and 5.56 Military Cartridges
There is a general misperception by the shooting public that the 223 Rem and 5.56 Military cartridges are identical – just different designations for commercial and military – and can routinely be interchanged. The fact however is that, although somewhat similar, they are not the same.
• The cartridge casings of each have basically the same length and exterior dimensions.
• Mil Spec 5.56 ammo typically has higher velocity and chamber pressure than the 223 Rem.
• The 5.56 cartridge case may have a thicker sidewall and a thicker head - to better withstand the stresses generated by the higher chamber pressures. This, however, reduces the powder capacity of the case - which is of concern to the reloader.
• The 5.56mm and 223 Rem. chambers are similar but not identical. The difference is in the “Leade”. Leade is defined as a portion of the barrel directly in front of the chamber where the rifling has been conically removed to allow room for the seated bullet. This portion of the chamber is more commonly known as the throat. Leade in a 223 Rem. chamber is usually .085”. In a 5.56mm chamber the leade is typically .162”, or almost twice as much as in the 223 Rem. chamber.
• You can fire 223 Rem. cartridges in 5.56mm chambers with this longer leade, but you will generally have a slight loss in accuracy and velocity – compared to firing the 223 round in the chamber with the shorter leade it was designed for.
• Problems may occur when firing the higher pressure 5.56mm cartridge in a 223 chamber with its much shorter leade. It is generally known that shortening the leade can dramatically increase chamber pressure. In some cases, this higher pressure could result in primer pocket gas leaks, blown cartridge case heads, and gun functioning issues.
• The 5.56mm military cartridge fired in a 223 Rem. chamber is considered by SAAMI (Small Arms and Ammunition Manufacturers Institute) to be an unsafe ammunition combination and is listed in the “Unsafe Arms and Ammunition Combinations” Section of the SAAMI Technical Correspondent’s Handbook. It clearly states; “In firearms chambered for 223 Rem – do not use 5.56 Military cartridges.” Federal Cartridge is a member of SAAMI and supports this position.
• Federal’s XM193 packaging currently has a warning that states “For use in standard 5.56 Chambers. Do not use in non-standard 5.56 chambers.” This warning is also listed on the XM193 Product Specification Sheet. Winchester also has a similar warning on their USA brand 5.56 ammunition packaging: “Use only in firearms in good condition designed and chambered by firearm manufacturer specifically for this 5.56 ammunition and so marked on the firearm.”
• It is our understanding that commercially available AR15’s and M16’s – although some are stamped 5.56Rem on the receiver – are manufactured with .223 chambers. Our advice however should be that it is the customer’s responsibility to know what their firearm is chambered for and choose their ammo accordingly.
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Old August 1, 2010, 06:39 PM   #7
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I too have an SP1 I bought new back in 74, and its had many tens of thousands of rounds through it over the years now since, most of which were USGI or NATO marked 5.56, and its never missed a beat.

I've also shot a good bit of USGI/NATO ammo out of my Armalites and Bushmaster, and never had an issues with them either.
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