I just picked up my AR today from the dealer. its a blue label ,and the serial is MH 064XXX. I don't see anything that resembles a block.Would you guys be so kind as to fill me in on what to look for. The model is a 6601. Are there any pictures available so I know exactly what I'm looking for. As you can tell,I'm new to AR's. Were any blue label's made w/o sear blocks?

This question concerns the upper.I took the front pivot screw out to find out what size it is.I want to get a flattop in the future. Anyway,I pulled the frt pin out and inserted it where the rear pin goes.It fits,but its on the loose side compared to the front. The front fits snug. Would it be safe to say that I have a small hole upper? Thanks in advance for any assistance you guys can give!

CI, on the 6601 series the sear blocks were pinned with a blind pin pressed in from the right, assuming you are looking down on the lower receiver with the buttstock towards you.  Most of them were marked "Colt" and are easily discernible.  Since yours was pinned, it could have been professionally removed and left no trace, except for the pin.  There would be an odd hole on the right side above and to the rear of the hammer if the pin was left out.

To be certain, measure the pin sizes.  The large front pins are about .311 - .312 and the small are .250.

If you truly have a factory original, unlocked Blue Label lower with a mil-spec diameter front pivot pin, you have an object of value.

More likely, you are unsure of what to look for or a previous owner removed the sear block.

For comparative purposes, here is my Sporter Match HBAR with the sear block:



And here is my Sporter Lighweight that I removed the sear block from:



Notice the block is the piece marked "COLT" that fits inside the lower receiver just ahead of the rear take down pin.

As far as the size of the forward pivot pin, if you can even fit it into the rear take down pin hole, then you have a mil-spec size pivot pin. Sounds like you do indeed have a small hole pivot pin. Any standard upper receiver will fit without the use of adapters or conversion pins.

Quoted: CI, on the 6601 series the sear blocks were pinned with a blind pin pressed in from the right

The early Blue Label Sporters had the single pin on the right and two pins on the left (one above the selector and one below it) retaining the sear block.

Hey guys,

     I just want to say,THANKS A BUNCH! It turns out that my blue label is an early one, with the pin on the RH side. I saw a picture in a post of an AR for sale,and I recall seeing the pins on the LH side .That may be where I got confused. I'm glad you guys straighened me out. Also,after more checking,this rifle is UNFIRED! I'm happier thana pig in .....!

Quoted: It turns out that my blue label is an early one, with the pin on the RH side.

Just to keep the record straight, sounds more like your Sporter is from later in the production run. ALL Blue Label guns had the sear block pin on the right hand side. The earliest Blue Label Sporters had two pins in the left hand side in addition to the pin on the right hand side. I probably wouldn't even bother attempting to remove the 3 pin style sear block from an early Sporter. Looks like it would be a real pain in the ass.

Nice score, though.

Thanks, Boomer.  I have never seen one with the pins on the left side.