46.0 gr. Rx 11 with a 165 gr bullet for 2739 fps at 46,000 cup.
41.0 gr. Rx 11 with a 168 gr bullet for 2518 fps at 38,100 cup.
Reloader 21 was one of the slowest powders made back then and as stated before not suitable for use in the Garand.
If you open the Rx11 and the powder is a nice dark color with no brown or rust color showing and doesn't not have a strong acid smell then the powder should be OK to use but only you can decide that.
That is what my old data states also. The RL21 is indeed too slow for the M1 Garand.