Want to know when and on what models did Colt go to the large fire control pins. Looking at a 6601 but the guy can't figure out what "big pins" means. Any help would be great. Bighammer shows production on the 6601 started in 1991. I know Colt played grab ass when it came to consistency but if you got a call on this one let me hear it. Mike

Like you said, Colt made a real mess of things when they did the switch. There is no hard and fast rule to go by.

But...you can generally go with this. If the receiver has the large pivot pin then usually it will have the small fire control pins. If the receiver has the small (standard) sized pivot pin then it usually will have the larger sized fire control pins.

I don't think I've heard of anybody who had a receiver with the large pivot and fire control pins. But the way Colt did it, there may be a few out there.

Colt did let some small pivot pin receivers out with the small fire control pins. There aren't many, but there is a very small outside chance the gun you're talking about has these.

Good luck.

Which pins (receiver and fire control) are mil-spec, and like the ones on every other AR-15 clone.

I had a colt 6601 HBAR fuyll size rifle.I eventualy traded it for a then current production bushmaster thats now a preban and turned into a carbine.My colt had a fence around the mag catch but had a 2 screw front that was large and large fire control parts with the receiver block.It had the older dark gray finish cause my stocks,pisol grip and dust cover were black compared to the rifleI got it  a year after they started making ARs again with the new A2 improvements,I got it in 92 this way and paid $650+tax then for a year they stopped making it and I even traded ov the new at the time Bushmaster.