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The Colt forward assist appeared with the Sporter II version.
This probably means the rifle is an SP1 lower fitted with a later upper.
 

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Any other details? Is the upper A1 or A2?
Experts, why didn't Colt use the FA on the SP1? Or were they using up leftover uppers without the FA? ;)
Moon
 

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SP1 BCs were from M16 production, but their bottoms were machined back so they could not trip auto sears. SP1 uppers are somewhat different from M16 uppers. Not only do the front pivot holes have different diameters, but they have different center points too. Also, SP1 uppers are not machined out on the bottom for auto sear clearance.
 

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SP1 BCs were from M16 production, but their bottoms were machined back so they could not trip auto sears. SP1 uppers are somewhat different from M16 uppers. Not only do the front pivot holes have different diameters, but they have different center points too. Also, SP1 uppers are not machined out on the bottom for auto sear clearance.
Thanks, Dan. I knew about the different diameter takedowns, but had forgotten that they were drilled on different centers. Now that you say it, I recall cam-looking pins that were marketed to allow mating uppers and lowers with the pin issue.
I'm glad Colt has gotten over the wretched excess about full auto conversions. It would seem to me that ten years in the pokey should be disincentive enough.
Moon
Moon
 

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Discussion Starter #8
Thanks for the input. I went ahead and bought the SP1 knowing that is probly an aftermarket upper. Its an A1 upper with FA. The button on the FA is tear dropped shaped. I got it from the original owner who claims he purchased it in this way new from a dealer in TX in 1978.
 

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Hey guys, just wanted to let you know there's a bit of SP1 coverage in the latest American Rifleman. Good read for Colt/M16/Vietnam war buffs and, of course, vets of the era.

Mike H.
 

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Pictures? When did you get the rifle? Do you have a letter from Colt stating that it originally came from the factory with an M16 upper receiver? What does the front pivot pin look like?
 

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Your last picture shows an after-market eccentric front pivot pin adapter, not a Colt one. Colt did in fact market an eccentric pivot pin adapter, but it had large screw heads on both sides. The Colt adapter came with the LMG heavy barrel kits that were sold about 15 years ago. I believe these heavy barrels were made by Colt Canada. Be that as it may, the eccentric adapter shown in your picture is NOT, I repeat NOT, of Colt manufacture.
 
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