I found a published load in "The Complete Reloading Manual for the .30-30 Winchester" in the "Speer Bullets" section 150 gr. H4895 MIN: 27.0 grs. 1674 f/s MAX: 31.0 grs. 2041 f/s.

Unless you found a published load for 20.5 grs., would add 6.5 more grains. Going below MIN. is just as dangerous as going over MAX. Good luck.