Sounds like you maybe putting a little too much expansion on the cases. You can lubricate your brass with Hornady One Shot Case Lube to reduce the effort needed. There will still be resistance felt on the handle. I find One shot works well.
You can use the same bullet you use in you gun for both .38 special and .357 mag. Depending on how hard the bullet is will possibly determine how hard you can push them in the magnum loads. I use mostly jacketed bullets for my loads and use the same bullets for both.