Lee will make you a custom size die for $25. That's the easy route. .410 to .425 is a lot farther than I would try to open one up. Two to three thous is about as far as I go. If .425 is the final size you want, you might want the die to be .423 to allow for springback.
You may not need the custom die. I dunno how big a bulge you are talking about or how tight your chambers are, but I'd shuck a few through a common .429 size die and see if they worked. Even if I were gonna size them down more, I'd use a .429 as a first step.
