Re: 270 stw
Well, it seems if you look at the next smaller cal. ( the 270 roy) you will have start data in this case. There are some 270 stw shooters here that'll be able to get more specific but I've had to do similar with the 7rem/7stw/7rum on a few occasions.
Example: With the 7 rem and a 140, 68-70 of rl22 is tops; and it's a start charge in the 7stw. Be very careful as it is a rather rough approximation.