SP1 / AR15

[Moderator]

Anyone know if an AR15 upper will fit on to an SP1 lower?

 

[cdkayak]

It should fit fine. I have an SP1 upper on a new lower without any problems. What you'll need to check are the takedown and pivot pin diameters. The proper diameter is .25". There were some Colt lowers that had a different pin size for civilian sales.

CD

 

[Lynne]

I'm moving this to the Firearms/Equipment/Ammo section.

Mother

 

[Moderator]

Thanks, Ma

 

[PatMcD]

A regular (non Colt) upper will need a special busshing screw to fit on a SP1 lower. The Colt lower has a large hole and the AR upper has a standard small hole.

 

[M1911]

The later colts have a larger hole. But is that also true of the SP1? Didn't that have a small whole?

 

[Nickle]

The newer (A2) Colts are MILSPEC. SP1's are NOT MILSPEC. The Pivot Pins and Trigger Pins are different diameters than the MILSPEC parts.

 

[cdkayak]

I wasn't aware the FCG pins were different on the SP1's, that's good to know.

I have seen both 'large hole' and 'small hole' lowers that were listed as SP1. The upper I have was also sold as a SP1 but it has the small holes.

CD

 

[Ericman]

So If i live in MA and have a Sp-1 (obviously preban) I am allowed to put current production uppers with AW features (threaded barrel, bayonet mount, etc)?

 

[FunYun]

All that maters is that the lower was assembled into a firearm before Sept '94. What you do with that lower afterwards only needs to comply with NFA.

 

[PatMcD]

The large hole we talk about is .315". Standard, or small hole is .250".

The upper I have was also sold as a SP1 but it has the small holes.

CD

Chris, the upper you have may be a M16 upper, which would have the standard small holes. Except for the holes, a M16 and a SP1 upper are the same (except for the bolt, too).

Colt was playing it safe, I guess, back in the 60's and 70's when the SP1 was out. They didn't want full-auto uppers or lowers to be used on their commercial rifles.

I use a SP1, slick-side lower on my spacegun. Had to find a Jewell trigger with the large pins and also get the the offset bushing, but after that, you're good to go.

 

[Moderator]

Thanks for all the info everyone.

 

[cdkayak]

Chris, the upper you have may be a M16 upper, which would have the standard small holes. Except for the holes, a M16 and a SP1 upper are the same (except for the bolt, too).

You're probably right, it was unused with some cosmo still on it & the bolt carrier group had been pulled.

 

[Nickle]

Well, if it's small pin, then it's probably MILSPEC, and then your problem is solved.