Mixing up those two bullets isn't nearly as risky as mixing up those two powders.
16.7 gr of HP-38 would surely put you into a high pressure area. As you've indicated, it's always best to only have one set of components out at a time.
on edit: I'm not suggesting the OP loaded the round with HP-38. Just reminding that it's good practice to only have one powder and bullet weight out at a time.