I can do 30 without a wad if I use grease over the balls. With a greased wad, 25 puts the end of the ball pretty close to the end of the cylinder. I believe I once loaded 30gr with a wad and was shaving a little lead as I rotated the cylinder through. It's most accurate with around 22gr of 3F or Pyrodex P.
I found that both my NMA and ROA have their more accurate loads about that percentage under max like yours. I have a new adjustable measure that allows me to work in 2.5 grn increments so I’ll be reworking both guns to find their best loads so I can reconfigure their universal bullet design that looks close to 230 grns so far.