I have two Colt lowers that I bought during the ban. Since I am in a free state, I am looking at selling both of them. I also currently have a post ban Bushmaster lower. While taking the Colt lowers off, I compared them to my Bushmaster. In holding them next to each other, Bushmaster to Colt, there are only two differences that I can tell. Three if you count the large hole on the Colts. 1- My Sporter Match HBAR has a small hole in the bottom of the reciver, on the inside. The Bushmaster and the older Colt do not have this. Anyone know what this is for? 2- If looking down into the lower, starting from the back going forward, there is a channel cut in that then narrows down before getting to the FCG. On both Colts, on the right hand side of this channel, where it narrows, there is only what I can describe as a "blurp". Any thoughts on this? Thanks in advance.

COLT without hole.


COLT with hole.

different specs.

I'm in a ban state and might be interested in one of your lowers.

Different specs, probably. Does anyone know for what purpose. One has a hole in the bottom, one doesn't. Both have what, in my industry would be called "drill wander" on the right hand side. I will get a pic of my BM tonight.


IM sent west.

Quoted: Different specs, probably. Does anyone know for what purpose. One has a hole in the bottom, one doesn't. Both have what, in my industry would be called "drill wander" on the right hand side. I will get a pic of my BM tonight. IM sent west.

Don't know what your industry is, but that "drill wander" is intentional machining by Colt of all AR lowers of that era. It was intended, I believe, to discourage at least one form of drop in auto sear from being used; though I don't think it stopped a whole lot of people.  The thicker wall pertion just ahead of it was also part of the "discouragement".

Quoted: Quoted: .....It was intended, I believe, to discourage at least one form of drop in auto sear from being used; though I don't think it stopped a whole lot of people.  The thicker wall pertion just ahead of it was also part of the "discouragement".

Would that one form of auto sear be something that didn't have a Colt name on it? Sounds different then what I was led to belive when I bought it. Green Label lower's were "supposed" to be easier to get to full auto.

Quoted: Quoted: Quoted: .....It was intended, I believe, to discourage at least one form of drop in auto sear from being used; though I don't think it stopped a whole lot of people.  The thicker wall pertion just ahead of it was also part of the "discouragement". Would that one form of auto sear be something that didn't have a Colt name on it? Sounds different then what I was led to belive when I bought it. Green Label lower's were "supposed" to be easier to get to full auto.

I'm really not too comfortable talking about what is and/or is not an "easy" conversion  Lets just say that the add on steel sear blocks that came along were Colt's next generation attempt to keep people from converting ARs to select fire.

Quoted: I'm really not too comfortable talking about what is and/or is not an "easy" conversion  Lets just say that the add on steel sear blocks that came along were Colt's next generation attempt to keep people from converting ARs to select fire.

Full atuo. Heard just gotta file down the doo-hickey there.

Steel sear block, not that sounds familiar. Could that be what the hole in the bottom of the one rifle was for? Thanks for your help.