Preban Colt Lowers

[kevblah]

Hi all, I’m in the process of doing my research for an AR build and one of the routes I’m considering is getting a preban colt lower, stripping it and building on it.

Now I’ve done a lot of searching and reading and from what I can tell, these are the “incompatibility” issues I may run into with modern day uppers and components, but was hoping those more knowledgeable can provide clarification.

1. Sear block - will interfere with all modern day bcg’s and some triggers, namely geiselle? Shaving off the top of the block (diy) will allow a full bcg, but for the trigger you need someone to mill out the entire block?

2. Larger front pivot screw. From what I can see, there are offset pins that will allow you to connect a preban colt lower to any modern uppers pivot hole?

3. Larger trigger pins? I guess some triggers have large trigger pin models to solve this but otherwise normal triggers won’t fit?

These are the three possible “incompatibilities” I have found in my research but do all preban era colt lowers have all three of these things? Or are there some that don’t?

Thanks in advance

 

[PappyM3]

Hi all, I’m in the process of doing my research for an AR build and one of the routes I’m considering is getting a preban colt lower, stripping it and building on it.

Now I’ve done a lot of searching and reading and from what I can tell, these are the “incompatibility” issues I may run into with modern day uppers and components, but was hoping those more knowledgeable can provide clarification.

1. Sear block - will interfere with all modern day bcg’s and some triggers, namely geiselle? Shaving off the top of the block (diy) will allow a full bcg, but for the trigger you need someone to mill out the entire block?

2. Larger front pivot screw. From what I can see, there are offset pins that will allow you to connect a preban colt lower to any modern uppers pivot hole?

3. Larger trigger pins? I guess some triggers have large trigger pin models to solve this but otherwise normal triggers won’t fit?

These are the three possible “incompatibilities” I have found in my research but do all preban era colt lowers have all three of these things? Or are there some that don’t?

Thanks in advance

Those are the ones, but not all Colt lowers have all of them. Note that the front pin adapter is still not a quick pull out and requires unscrewing it. It is not nearly as quick of a changeover as the normal pull pins if you want to swap uppers a lot.

Old slab sided SP1s only have the large front pivot pin. They have normal trigger pins and no sear block.

Most preban Colt lowers with fenced sides have all three incompatibilities. And there are a couple different types of sear blocks.

However, there is one particular preban lower with fencing on the side that also had a normal front pivot pin. The sear block is easy to remove and Geissele makes large pin triggers (albeit at a premium) There aren’t a lot of these lowers and can be hard to find. But they are the closest to mil spec for someone who wants to change uppers a lot. Someone else will have to chime in on that model/date range though. I don’t recall off the top of my head.

Or, you can just get an Eagle Arms, Bushmaster or other good quality preban that’s fully mil-spec.

 

[dw617]

If you'r stuck on a Colt for some reason, get a slab sided SP1/SP2 with no sear and normal trigger pins.

 

[DarthRevan]

I have a Sporter 2 that only has the front large pin as a weird feature, and the offset works well enough. You may need to trim your hand guards to get it to fully open though without unscrewing it every time. Hopefully I can buy a NH house within the year so I can sell the colt.