AR15.Com Archives
 Mil Spec Colt Lower
424v8  [Member]
7/11/2001 10:01:25 PM EDT
Maybe this issue was addressed before but still like to know if Colt ever make a preban lower that has all the Mil Spec like a Bushmaster lower. This includes raised fence with pin hole drill for detent, small front pivot, mil spec trigger group with no sears block. If Colt made this lower then what's the model #. Thanks for any input.
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Circuits  [Member]
7/12/2001 12:22:00 AM EDT
There is no specific model or serial number range, but at some point, when colt switched from green to blue labels, there were a number of unblocked, small-pivot, small-firecontrol A2 reinforced lowers produced. After that, Colt went to small pivot pin with sear block, and after that to small pivot pin with large fire control pins.
Mean_Green  [Member]
7/12/2001 10:05:53 AM EDT
There is one for sale at

GA# 976114812

$2250 bones
rhatland  [Member]
7/26/2001 6:49:20 AM EDT
I purchased a Colt HBAR in 1993. It appears to have small hole upper. I want to know how to determine if fire control parts are standard Mil Spec or not? Also, I want to remove my upper and sell it;however, I need a replacement front pivot pin for any new upper I purchase. Does Colt make one or do I need to go to bushmaster?
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Fox  [Team Member]
7/26/2001 12:19:20 PM EDT
rhatland, if you have a small front pivot pin it will measure .250 in diameter. The large pins will usually measure .311 - .312. I have never seen a blue label rifle (which is what you have) that has Mil-Spec fire control parts. The small pins are .154 and the large .169. To measure them, just push your hammer or trigger pin slightly to one side, just enough to measure with the blades on a set of calipers.

Why do you need a replacement front pivot pin? Do you mean an offset pin to match a large hole lower and a small hole upper? I know that BM carries both sizes of fire control pins. You just have to specify when you order. I do not know if they carry the large front pivot pin.
rhatland  [Member]
7/26/2001 12:26:19 PM EDT
I have a screw type front pivot pin and when I remove it, I do not want to use it for my new upper. I am planning on getting a new small hole upper to mate with my small hole lower. I just do not want to use my Colt screw type front pivot pin. Secondly, I do appreciate your comments. I am unsure of what constitutes fire control parts. I assume everything that makes up your lower receiver parts. Also, are military size fire control parts (not M16 parts) able to fit into my Colt? Thanks.
Fox  [Team Member]
7/26/2001 12:52:55 PM EDT
rhatland, fire control parts refers to the trigger, hammer, disconnector, pins, safety and springs. Colt typically used the non Mil-Spec (large - .169) pins for their commercial rifles. Bushmaster on the other hand has always used the Mil-Spec (small - .154) pins in their lowers. Therefore, if you have large pins, which I am almost certain of, you cannot use Mil-Spec pins in your rifle. Colt also used the screw type front pivot pin in both the large and small versions. To make matters worse, Colt did not drill most of their lowers for the detent and spring, which holds the standard front push-pin and prevents it from being pushed out of the lower. You will need to check your lower to see if it has been drilled. If so, you will find a small hole drilled into the mag well between the front pivot holes on the lower, near the right hand pivot hole. If there is no detent you cannot use a Mil-Spec pivot pin. Your options are to have the lower drilled, stick with the Colt screw model or use one of the after market pins with a built-in detent.
rchurilla  [Member]
7/27/2001 6:55:43 AM EDT
"Colt" and "Mil-Spec", 2 things that have no business being in the same sentence.

Nothing personal against Colt, but if you buy anything other than a Colt, you won't have these problems. Wrong sized pvot pin, different sized hammer and trigger pins, "blocked" lower receivers etc.

DON'T BUY A COLT. You'll be sorry in the long run.

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