My 38/55 was set up for Black Powder. Wanted a practice load shooting to the same sights. Used 17grs of 4759, when it was discontinued switched to 17 grs 4227, no wads. Charges thrown into a scale pan from a Harrell’s measure, check weighing, pass or dump & throw another. It’s possible  to  throw a light charge working the measure too fast. Want piece of mind all have the same point of impact, weighing does that. 

Rarely use BP today, main match does not require it .   If I could not get 4227 would use 4198 and a bit more powder, same methods. 

Boats

I have two 38 molds. Original mold when CPA built the rifle 1993 was a LBT two cavity 290 gr spritzer. Was waiting for a Barnett that never arrived Veral delivered the 290 quickly. Dozen years later switched to a Hoch round nose single cavity 305 gr. 

Offhand shooter monthly matches & couple practice sessions it’s high volume. I used to practice with 245 gr store bought bullets shoot the 305 Hoch in matches. There is no score difference offhand 200 yards 245 or 305. Winter cast a lot of 305 run out switch to the 245. Grandsons learning offhand with that rifle & it’s .22 barrel. # of CF rounds fired will go up considerably soon 

I use 17 grs 4227 all three bullets. Also my 1993 barrel is slower twist that what’s common today. Doubt 330 grs often used today would be successful. 

Your 270 ought to be fine, our club matches don’t, allow Gas Checks if they did I might use them . Often use a 1903 30/06 Arsenal built Sporter practice 208 gr gas check 18 grs 4227 it’s a very good combo 200 or 300 yards.

Boats