I'm not sure where to post this so I posted it here as well.

I have a rookie question. I have a pre-ban AR15 9mm-nato with a serial TA0. The carbine was from the 80's. It has a screw instead of a push pin in the front pivot. Can someone tell me if this is an off set? Did Colt make it this way for a reason? Are they supposed to be small or large pins?  I am turning it into a SBR and need to know if a RO635 upper will fit on the lower with out any modifications?

If you don't get a good answer here you could post this at the Industry - Colt forum where all the Colt guys hang out.

I'm not too familiar with 9mm models but you could unscrew the pivot pin and look what is the size of it.

Should be .250" DIA for small Mil-Spec size pins, if it is larger than this there are conversion pins available from CDNN or even specializedarmament.com (higher cost).

If it is a small pin, look at the right side of the pivot hole in the lower receiver and see if there is a small hole for the push pivot pin detent.

If you have this small hole for the pivot pin detent, you could buy the push pin, detent pin and detent spring and you could convert it if you want to.

No pin detent hole, it can be converted if you wish by ADCO, they also provide and install the push pivot pin set.

Thanks Alpha. I'll contact ADCO. I'll also post in Colt fourm. I just curious as to why Colt did it this way?

Quoted: Thanks Alpha. I'll contact ADCO. I'll also post in Colt fourm. I just curious as to why Colt did it this way?

There is no consistent way with Colts, once you think there is a pattern, then you get surprised with some exceptions to the rule.

My new 6721 A3 tactical carbine I bought last year came with a screw type pivot pin from the factory, but luckily it have the pivot pin detent hole and I just bought the parts set and installed it myself.