CDNN has Colt SP1  uppers for $399.00  ( NO BOLT OR CARRIER) BUT A FREE STOCK AND SPRINGS.)
Used Colt SP1 for $299.                              "         ""       "                   "                       "
Used (other) mnf. $269.
What is an SP1.... and is this a good deal.

First of all, what CDNN is selling are NOT SP1 uppers.  They're M16A1 military surplus pieces---and that's a good thing.

The Colt SP1s were the first civilian market ARs, and the front mounting hinge holes were larger than the military standard.  Current commercial lowers use the same 1/2 inch front mounting diameter as the military has always used, and if you did try to put an SP1 upper on a current lower, you would have to use an adapter sleeve to make it fit. What CDNN has will fit any currently built lower w/o any adapter needed. Also, the pieces CDNN has are forward assist M16A1 types, and the SP1 did not have a forward assist assy.

The CDNN pieces are apparently takoffs from new, unused M16A1s, and everyone who has gotten one and posted on this site about it has been happy w/what they got. It should be noted though, that the early pieces were finished in a different, lighter color than is current standard, so if you intend mounting one on a currently built lower it will have a two tone finish

Re the price, you'll have to decide if the assy is worth it to you. On the plus side, it is a Colt assy, and top of the line. Remember though, these units have the early, lighter weight barrels, and the flip type rear sights; as opposed to the current click adjustable type.  You can build up an aftermarket A2 type upper for not much more money, but of course it won't be a Colt---if that matters to you

Why CDNN insists on calling these pieces SP1s is beyond me.  My only assumption is that they're afraid that if they call them what they are, M16A1 uppers, some nutcase will accuse them of selling "machine gun parts"

Very happy....

I've been thinking about one of these, with a Stag lower, bolt and carrier....

Quoted: ...Current commercial lowers use the same 1/2 inch front mounting diameter as the military has always used,

You mean 1/4"  right?

I did mine with a DPMS lower and finished it with Norrells

yeah i'm thinking about grabbing one of these as well, to build on one of my RRA lowers.  hmmmm.

has anyone bought the used (lower price) upper and how does it look?

Quoted: Quoted: ...Current commercial lowers use the same 1/2 inch front mounting diameter as the military has always used, You mean 1/4"  right?

Whoops. The typo gremlin strikes again.

I bought an M16, slab side, refinished, upper through the below link.  I am very happy with what I got: perfect for my lightweight CAR build.

ar15.com/forums/topic.html?b=7&f=119&t=276645

I'm assuming that any quality bolt and carrier assembly will work with this upper.  I had an original SP1 before forward assist and all that I bought in 97 for $300.  It was basically brand new, original owner had passed away and it had been in a safe for 22 years when I bought it.  Could barely tell it had ever been shot and I sold it a few years ago for about $1300 so I wouldn't mind having another to replace it with.  Thanks. gS

I am using a RRA bolt and carrier

Thansk KJoe. gS