AR15.Com Archives
 Are the old Colt AR-15 SP1 rifles chambered for .223 or 5.56mm?
cantgrowup  [Member]
5/3/2010 4:10:19 AM
I can't remember.
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osprey21  [Life Member]
5/3/2010 6:35:56 AM
My 4 digit serial numbered gun is marked .223
crackedcornish  [Team Member]
5/3/2010 6:59:31 AM
chambered in 5.56
RLR350  [Team Member]
5/3/2010 7:41:52 AM
The newer SP-1's receivers (1980's) are also marked .223, however it is only a marking and as crackedcornish stated they are chambered for 5.56 (or both).

Here is an article that explains it. Somewhere in it is a line to the effect of "Colt recognizes no difference between these two “caliber” designations" although they mark their receivers and mags differently for other purposes.

http://www.specializedarmament.com/content/skins/flat/popup_issue_100.html
Hal143  [Member]
5/3/2010 8:17:03 AM
I think they were marked .223 because back in the day 5.56 was not available to the public. Correct me if I'm spreading internet rumour.
I may or may not be full of BS.
cantgrowup  [Member]
5/3/2010 8:39:19 AM
So... even if my SP1 is marked .223, it is actually chambered for the 5.56mm and can safely fire milsurp ammo?

I'm away from home for a month and can't check my barrel/receiver to see what my SP1 says. I know all of my other AR-15's from other mfgrs are marked 5.56mm. I never shoot my SP1 anymore, but just wondered if it is safe to fire 5.56mm in it.

Thanks.
Hal143  [Member]
5/3/2010 8:47:26 AM
Originally Posted By cantgrowup:
So... even if my SP1 is marked .223, it is actually chambered for the 5.56mm and can safely fire milsurp ammo?

I'm away from home for a month and can't check my barrel/receiver to see what my SP1 says. I know all of my other AR-15's from other mfgrs are marked 5.56mm. I never shoot my SP1 anymore, but just wondered if it is safe to fire 5.56mm in it.

Thanks.


People have been firing 5.56 mil-surp in SP1's since it's inception. Just make sure your rifle is clean and in good working order.

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