I have a Colt HBAR I bought in March and I want to have an upper receiver to change out from the standard A2 it came with. I've heard that Colt's take down pins were different size's than every one elses, I'd like to have a varmint upper for it, just to tinker with. But I want to shy away from buying from Colt only to getwhat I want.
Look forward to hearing from all of you.
Semper Fi,
Keith
Sgt USMC

Welcome aboard Keith.

Is your HBAR a new production piece or an older pre-ban rifle?

The front pivot pin on the pre-bans were a larger, unique size. On the post-ban and current models they used the standard size pivot pin, which of course is the same size as the rear takedown pin.

You can use an upper receiver assembly from anyone on your lower receiver. If your rifle uses the standard pins then all you need is the new upper assembly. If your rifle uses the older, larger pivot pin then you can get an adapter pin from whoever you get the upper assembly from to adapt the two different sized peices.