18DAI, I also have a 3 inch 66-4 with the BUH prefix. Mine is non-ported, with the sight ramp running all the way to the frame. The only distinguishing feature about mine is it is double action only with a bobbed hammer. Hammer and trigger are both case hardened. It appears to be factory, but I do not know as I am not the original owner.

I had a gentleman look at mine once who had a notebook with a bunch of information written in it. After examining it he told me he thought it was one of a run of 12 that was made for the New York City Transit Police in double action only. It has no markings from any agency. I suppose I should get it lettered to see if Roy can enlighten me.

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Expect no quarter.