Just so you know...
lead bullets generate HIGHER pressures than jacketed. I think its that the bullet seals off the bore better, and the soft metal drags more, but lead makes MORE pressure, not less.
It's counter to what I used to assume, but such is the way of the world.
If you are getting more velocity, you are generating more pressure (all factors being equal). There ain't no free lunch, it has to be that way.
Start with the starting loads. One, or several hundred overloaded rounds won't blow up the gun. Unless it's a cataclysmic level overload. However, a diet of minor overloads will beat your gun to death much sooner.