I'm looking at a preban 20" that is s/n MH something. It is definitely preban but I don't remember the serial number, just that it starts with MH. At least that's what I recall. The barrel is marked out in front of the handguards with something like C MP 5.56 etc. and what I want to know is if anyone knows definitely if this is large or small pin. If I get it I want to put my Dissipator upper on it until I can get another short upper. Thanks for any help on this.

I have no idea [:)]

Since it is a "Match" serial number, it is likely a small pin, but Colt did all kinds of mixing and matching, so your best bet is to open up the rifle and measure the pivot.  Small is 0.25", large 0.315" or so.

Sounds like a Match H-bar...I had one awhile back and it was a large pin.

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