OK, I found that with a 26"-14 Twist tube that mine actually would not shoot flat based bullets as well as Boat tails. Mileage may differ.
You've also been playing around in the same burn rate area on powders and it just isn't working for you.
Since you say that you've used 380, I would go to either H-414 if available, or AA2700 which is available. They are slower than what you are using now.
AA2700 gave me the best results for accuracy/velocity of all the powders you mentioned other than 380, but it wasn't as temperamental at the top end on hot days as 380.
There are loads out there for the Swift that do go the other route as in faster powders i.e. Benchmark, H-335 range, but I wouldn't recommend going there since you are having trouble now.
Might even try a mag primer w/380. sometimes that helps also.
