So long as the lead is soft enough to obturate to the bore I doubt you would see a difference. Hard V soft is namely going to be a performance difference in driven velocity.
All i use are Penn bullets for pistol lead. If your staying under 900 to 1000 fps you will be fine using standard lead. I use his hard cast for 44 mag including rifles over 1600 fps. What 38 bullet are you considering?
I, too, favor Penn, they make good bullets.
Bullet diameter matters as much as the alloy.
You might want to just ask the folks at Penn for a recommendation.
If anyone should know....