Stag Arms Lower + SP1 Upper

[Soap]

Does anyone know if the Colt SP1 upper is compatible with a Stag Arms lower? The reason why I ask is because IIRC the A1/A2 pin sizes are different. Any help is appreciated.

 

[Kaylee]

For what it's worth, the M16A1 upper I got from CDNN a while back fits a stag like it was one piece of metal.

I don't believe there's an A1/A2 difference but rather a "pre Colt being PC/post Colt being PC" difference. I'm afraid I don't know when the cut off is though.