This is not unusual. Jacketed bullets should mike out at .429 while cast bullets at .430 to .431. When sizing, dies take the case back to original dimension or slightly smaller.
Your case neck expander will open the case mouth to the correct size and bell the mouth to receive the bullet. There can be tolerance issues in the dies themselves as well as case wall thickness issues that can create the bulge you are experiencing.
Or, it may be that your seating die is starting the bullet crooked.
So long as the cartridges chamber normally and accuracy is acceptable, it should not be a big problem.
Readjusting your case mouth expander may reduce the amount of your bulge. Also, some dies come with 2 seater plugs, you may need to try the other seater plug if your bullets are being started crooked. Hope this helps.