1829 Dimes are found with Curl Base 2's and Square (or Flat) Base 2's. A subset of the Square Base 2's is the "Medium 10C" variety. The Medium 10C is distinctly different from the Small 10C, the Large 10C, and the Extra Large 10C (use the attribution illustration for help in differentiating them). Two die varieties make up the Medium 10C subset: JR-11 and JR-12. Both are scarce, though the JR-12 is slightly less so.
The 1829 Medium 10C is fairly easy to obtain in Mint State. The PCGS Population Report shows approximately a dozen examples that are MS65 or better, plus sufficient supplies at the MS62 to MS64 levels. The finest example is a single PCGS MS67.