I have a colt 7.62x39 upper with barrel marked c mp 7.62x39 1/12 H Bar. what do I need to do to convert this over to .223? I believe it is pre ban. any help is appreciated

I dont think you can rechamber them easily. Its probably cheaper just to buy a new upper. If you have a PRE-BAN gun you can put a preban upper on it. But it (your original gun) must have been assembled into a COMPLETE gun BEFORE the ban. If it was just buy a new 5.56 pre ban upper.

A new barrel and a new bolt will be required....
You will need a barrel wrench and a receiver block and insert to clamp the receiver down. If you don't you may warp the receiver....

The upper is worth $450 to $500 (maybe more depending on condition)with the BC and you would be able to move it fairly easy on AR15.com or the strumgewehr board. Then you could get a factory assembled upper for that price and not fork out the cash for the tools...

Good luck..

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I'd sell the 7.62 x 39 upper and use the money to buy a new 5.56 upper.

As pickupdan said, you can get a nice new factory upper for that price and not have to mess around with buying tools and possibly buggering up the assembly.