Mom -
The 9x19 is a high pressure cartridge and nothing to be taken lightly. You are right to ask questions.
• While it is
generally correct that you can substitute one 115gr jacketed bullet for another 115gr jacketed bullet, in this case the second bullet is almost .020" longer. This means it will seat
deeper at the same OAL, thus
raising the chamber pressure. Raise by exactly how much is a guess. Thus....
• It is accepted safety practice to start again at the starting load and work your way up to be sure you do not have more chamber pressure than you planned. This is the only true safe way to load with a new bullet.
• However, seeing as how it's the position of the bullet's base that has one of the largest affects on pressure, if you were sure that the stated load was very far down the load range (sorry I'm not looking at a book to confirm) then you might simply try seating the bullet with +.020" on the OAL (iow 1.120" in place of 1.100"). But they would need to be tested for proper chambering using some "test cartridges" built-up using
no powder and
no primer.
The above graphic explains why you want to think in terms of seating depth, and not OAL.
I think you intuitively sensed that, and that's very astute of you. Of course, seating depth cannot be directly measured, so we simply throw around the term "OAL" like it was
magic. However, you have the opposite issue shown in the graphic. Your new bullet will be deeper than your previous reloading efforts.
In "all things reloading" try to err toward safety.