Shooting 5.56mm in a Colt SP1

Colt just did that because they didn't want military designation on their civilian line of rifles. Also at the time you could only by .223 ammo. There was no surplus or manufactures making 5.56mm.
 
Safe to shoot 5.56mm in a rifle chambered for .223 Rem, pressures are lower in 5.56mm.

Not always safe to shoot .308 WIN in a rifle chambered for 7.62mm, pressures are higher in commercial .308 WIN ammo than NATO 7.62mm.
 
Not trying to be a #### but how does this thread come up especially when I look at some of the profile on here with there join dates going back over 8 years. How do you guys still screw this up. Lol. Its feels like the usually questions we got back in 1996 ??

Your colt SP1 will be fine with military grade 556. Yes. As Rebel said they just marked them 223. Some manufactures still do that today I suppose. Stick to colt.
 
bellero said:
Safe to shoot 5.56mm in a rifle chambered for .223 Rem, pressures are lower in 5.56mm.
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Nope. Pressures are higher in the 5.56; however, shooting 5.56 in a .223 chamber will be operating at the upper end of 5.56 rated pressure (around 60k psi, which is the max pressure for the cartridge, where 5.56 in a 5.56 chamber usually operates closer to 58k psi). Generally this will not lead to safety concerns as the bolt thrust is still well within its safety margin, but you will have slightly increased wear on the throat of the chamber. I wouldn't recommend interchanging in a rifle with a .223 match chamber, but in autoloaders like AR's I wouldn't be concerned about it (most of them have hybrid chambers these days anyway). One other note is while SAAMI considers .223 and 5.56 to be non-interchangeable, CIP considers them the same cartridge, so European rifles marked .223 are built to shoot 5.56.
 
Ar180shooter said:
Nope. Pressures are higher in the 5.56; however, shooting 5.56 in a .223 chamber will be operating at the upper end of 5.56 rated pressure (around 60k psi, which is the max pressure for the cartridge, where 5.56 in a 5.56 chamber usually operates closer to 58k psi). Generally this will not lead to safety concerns as the bolt thrust is still well within its safety margin, but you will have slightly increased wear on the throat of the chamber. I wouldn't recommend interchanging in a rifle with a .223 match chamber, but in autoloaders like AR's I wouldn't be concerned about it (most of them have hybrid chambers these days anyway). One other note is while SAAMI considers .223 and 5.56 to be non-interchangeable, CIP considers them the same cartridge, so European rifles marked .223 are built to shoot 5.56.
Click to expand...

Except the Colt SP1 is an actual 5.56 chamber, just marked .223. See Rebel's post above.
 
My last barrel on my M16A1 clone was an original Colt SP1 barrel assy.
I shot thousands of rounds of straight up Norinco 5.56mm 55gr FMJ in mine. It shot it fine, very accurately and never had so much as a stoppage.

BS on anyone who says it's not good to go.
It's a ####ing AR15 chamber, you think they cut it with a lazer? Shoot away. Just remember it's 1:12 so it won't stabilize 62gr FMJ. It may stabilize some 62gr soft points due to a shorter projo length.
55gr FMJ 5.56mm is optimal for the 1:12 Colt SP1 barrels. I swapped my old shot out SP1 barrel for a DA CQ311 brand new 20" barrel.
The barrel extension was a very tight fit in my upper surplus M16A1. Took a few persuasion whacks to the towel wrapped muzzle with a small rubber mallet to fully seat it.
The DA556 barrel is extremely accurate though. Much more than my Colt SP1 barrel was. I'm told they are cold hammer forged. Not bad for a $100 barrel! :rockOn:
 
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