1829 Zacatecas Mint, AO Assayer initials circulating contemporary counterfeit listed in Riddell's 1845 Monograph as #221.  Riddell-listed varieties are particularly collectible amongst the Cap and Rays ctft 8 Reales.  This example shows full details with some weakness at the bottom of the obverse.  I think this variety and example was struck on a German silver planchet but I've not completed elemental analysis to confirm this.