Assembling a pre-ban upper/post ban lower (Colt)


July 26, 2004, 10:54 AM
I've had these two Colt parts sitting around for years. With the AWB sunseting I believe it'll be ok to put a pre-ban upper I have on a post ban lower. The hole the pivot pin used to secure the upper to the lower (it's the pin that sometimes has a screw head on it) is different sizes; on the upper it's a bigger hole. Does anyone know who makes a pin that willl work to hook these two parts together? Is it important that the pivot pin fit snug? I could use a smaller in (one that will fit the lower), but then it wouldn't fit the upper hole and be snug.


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Fudgie Ghost
July 26, 2004, 11:27 AM
Fulton Armory has the pin you need. Just tell them what you're doing. Go to their site---I think it's called the "offset" pin.

Worked for me.

July 26, 2004, 12:14 PM

I went to their site and found this

1 FA-AR-200-254 Front Offset Pin, Large $5.95

I can't find a picture of it, so I sent them email describing my application. Hope it's the right one.

July 26, 2004, 01:09 PM
I hope that it works for you.

While there should be enough clearance for the two half to rotate on that front pin, the clearance between the upper and lower is crucial. That's because if it is too loose, the two halves will marry up fine, but it will affect the critical clearance at the rear of the receiver. This is where the face of the spring-loaded buffer plunger in the stock just "kisses" the rear of the bolt when you close up the two halves at the rear. That "kiss" is critical because it keeps that spring-loaded plunger off the little spring loaded "detent stop pin" that loaded into the rear-bottom of the receiver where the buffer tube screws in. When you shoot, and the plunger slams the bolt back home, the plunger travel too far forward and will whack against that little detent and break it off. ( That detent pin is designed to assist you when you pull the weapon apart by keeping the plunger in place and not launching into the stratosphere. Ask me how I know!) With the proper front pin clearance, the plunger kisses the bolt when you assemble the rear pin and prevents this "overtravel" of the plunger, preserving it.

I've tried different pins in my AR, using the ones I purchased from Bushsmasterl with only "ok" results. I have to assume that there is something out there that will work more effeciently but haven't found it yet. What I'm currently using is the small pin that fits the lower perfectly and and "eccentric" bushing in the large-hole upper that pushes the upper to the rear for the proper fit and that "kiss" I mentioned. It's a two piece affair which does tend to drift. I've secured my eccentic sleeve with some CA adhesive and it's held fine to-date.

Just thought I'd share the info.


July 27, 2004, 01:43 PM
I just rang them up - VERY helpful folks. For the Colts with the large hole upper/small hole lower they make a bushing that works. Makes sense, given the pin that goes into the lower is small compared to the hole in the upper. They're shipping the parts I need. Thanks for the pointer to them.

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