El Paso Saddlery has a nice River Belt/Tom Threepersons rig that would work well for your needs. Threepersons was an old time lawman from the horseback era. The belt is heavy enough that it would not fold up under use and light enough that it will be comfortable to wear. The holster would set fairly high and could be slid around on the belt to the place where you were comfortable while on horse back. Look at some photos of the rigs of around the late 1800's and copy them for your pistol.
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