But that shows a Remington 124-grain "MC" (Metal Case) bullet, which is different from either of the two Berry's bullets you might have. You haven't yet identified which one you have, and it does make a difference. One has a hollow base, the other doesn't. And Berry's recommends a different C.O.A.L. for each of the two.
And that doesn't call for 5 grains, it calls for 4.9 grains. The way the data are presented, that's the maximum safe load so, if we assume the data are still valid,
anything that would increase the pressure should be assumed to be unsafe.
Going back to the high school science class formula for gas pressure, P1V1/T1 = P2V2/T2. Since the two we would be comparing both involve burning gunpowder at a high temperature, for simplicity let's assume the temperatures are approximately equal and ignore T. So we want to compare the pressure change from the specified load to one with the bullet seated deeper. So the variable is the volume.
First we need to calculate the case volume. For the 9mm, Wikipedia lists a case volume of 0.862 cubic cm. That's .05260 cu. in.
Case length is (per Wikipedia) .754 in. Using the Berry's bullet from the on-line Hodgdon/IMR data, Berry's gives us a bullet length of .612 in.
The case length of .754 plus the bullet length of .612 adds up to 1.366. Hodgdon and Berry's call for a C.O.A.L. of 1.150", which means the bullet will be seated to a depth of 1.366 - 1.150 = .216 inches.
Bullet diameter is .356. Bullet cross sectional area is .10462 square inches.
.10462 times the seating depth of .216 means the seated bullet occupies .10462 x .216 = .02260 cubic inches. The remaining case volume is therefore .05260 - .02260 = .03000 cubic inches.
Now let's seat the same bullet to a C.O.A.L. of 1.000 inches. 1.366 - 1.000 = .36600" seating depth. Off the top of your head you can see that's a 50% increase in seating depth. So how much difference does that make?
.10462 x .366 = .03829 cubic inches, our new seating volume. So the new case volume behind the bullet will be .05260 - .03829 = .01431 cubic inches.
Again right off the top we can see that the new case volume (behind the bullet) is less than half what it was before. The formula is linear: Ignoring temperature, P1V1 = P2V2.
P2 = P1V1/V2
So the new pressure will be:
P2 = P1 x V1/V2
P2 = P1 x .03000/.01431
P2 = P1 x 2.09644
It's a rough calculation, that starts with the assumption that the combustion temperatures of the two loads will be close enough that we can ignore the effect of temperature. I'm comfortable with that assumption. What we see is that this "small" change in seating depth DOUBLES the pressure.
This is why (a) we don't exceed published load maximums, and (b) why it's so important to read and understand the complete load recipe. If the bullet you want to load is longer than the bullet in the published recipe and you load it to the same C.O.A.L., then you will be increasing the seating depth, which reduces the available case volume behind the bullet and increases the pressure.
Class is dismissed. Don't forget to turn in your homework assignments on the way out the door,.