Big pin, small pin Colt AR receivers and uppers?

[Cannonball888]

Hello,
Can anyone tell me if a 1970's Colt SP1 receiver is compatible with a USGI M16 A1 Colt upper. I am also interested in knowing what size takedown or pivot pins preban Colt uppers and lowers took vs post ban Colts?

 

[Jeff White]

No SP1 lower is compatible with any M16 upper. All of the SP1s had large double screw front take down pins. All M16s have small holes for use with small push pin take down pins.

You will need an adapter pin.

Jeff

 

[Cannonball888]

Are the late model Colt receivers compatable with M16 uppers?

 

[Jeff White]

Some of them are. It's hard to come up with a serial number cut off or model designation when they started using small pin lowers. All the current LE weapons have small pin lowers.

Jeff

 

[.45Guy]

They used to make funky offset screw slash/pins to mate the combo.

 

[yotesmoker]

sp1 pin

Now I'm getting real confused.I just got an sp1 and it has a small forward take down pin. The ser.# is sp198xxx. The selector is the 3 way ...safe...semi..and auto.The auto part has been deactivated but will fire semi in the auto mode.Just what kind of a sp1 do I have???

 

[rcmodel]

Well, I have an older one then yours.
Serial # SP120xxx.

And it had the big screw-type front pin until I changed it to a big push-pin, and a two-position SAFE-FIRE safety, just like every other SP1 I ever looked at.

I don't know what yours is, as I was not aware Colt had ever released any AR-15 with a three-position Selector marked lower.


rcmodel

 

[gcrookston]

There is an eccentric screw adapter that will allow you to mate a Colt Commercial lower to a usgi upper. check brownells.

 

[rcmodel]

Be very careful if you use it.

You can break the front pin hole clean off of the Colt lower if the eccentric pin gets in a bind when you open one up.

You should remove the front eccentric screw before you pop the rear pin to prevent damage.


rcmodel