I just ordered this A1 barreled upper from Kieth at CDNN, I ordered the one that says MISC. manufacturer (not Colt), for $269

The upper I got is an A1 configuration (with forward assist), it has a 3 prong hider on it.

The barrel has "RNC" stamped on it, it's a pencil barrel but appears to have a faster rate of twist than 1-12'(?) What's that mean?

The upper has a "C" in a square and a triangle above that, I think that means colt, but I didn't pay for the colt. Is it Colt?

It's odd that my slick sided M16 uppers all came with A1 bird cage FHs, while this A1 came with the 3 prong. The only time I've seen that was in the movie "Hamburger Hill". Can I get a little history on this.

Thanks.

Not sure what the RNC means, but the triagle square thing sounds like Colt proofmarks.   Your upper is probably a mixed matched upper assembly, and the receiver just happens to be a colt.  That would explain the MISC MFG and the lower price, since your upper isn't completely factory.

RNC is manufacturer and chrome chamber

How do you figure that it appears to have a faster rate of twist than 1-12?

Quoted: RNC is manufacturer and chrome chamber

Well, maybe only a chrome chamber.  Since it is apparently not a Colt barrel, which would have been marked C MP C, you really can't be sure what those markings mean.

It may well be fully chrome lined, depending on when it was produced.  My (clearly labelled) hunch is that it has a good chance of being fully lined, since replacement barrels by aftermarket suppliers would have come along a fair way down the production trail, when full chrome lining was standard.

Obviously though, the only way to be sure is to dab a Q Tip of instant blue on the bright edge of the rifling at the end of the barrel.  If the bluing doesn't take, it's fully lined.

Quoted: .........How do you figure that it appears to have a faster rate of twist than 1-12?

I looked down the barrel and tryed to follow a groove, it appeared to make a full rotation in about 8".

Quoted: Quoted: .........How do you figure that it appears to have a faster rate of twist than 1-12? I looked down the barrel and tryed to follow a groove, it appeared to make a full rotation in about 8".

When I try this I get dizzy.

I use a cleaning rod and bore brush. I marked it with a line down its length and one inch increments and pulled through and counted the turns. There is enough difference between 1-12 and1-9 or 1-7 to notice readily. You have to be particular and pay close attention to the turns to determine exactly what twist you have.

EDIT= I read somewhere the circle "C" and triangle stamp near the front of the port door mean the upper left the Colt factory as part of a complete rifle. Some people around here can look at the proof stamps on your reciever and tell you the week it was made from which side of the impression is heavier. But thats not me I just like to shoot.