So those that want as little bullet jump as possible are wrong?
As Painter said, it's not like it is with bench rest shooting at hundreds of yards out to a thousand. But even if it were crucial, you don't control that jump by having arbitrary minimum numbers. You control it by determining maximum OAL with every bullet, and deducting as much from that max for a working OAL as you choose. If that's .005, .010, or .015, OR nothing at all, you still get there by determining maximum OAL and taking a deduction. Having something like 1.12 minimum doesn't accomplish what you're trying to do.
One of my reasons also is case volume with particular powders not necessarily accuracy being my only concern.
Same idea as the previous. You control that by calculating seating depth: case length + bullet length - OAL = seating depth. You might think loading longer increases that case volume, but if you load longer than your maximum, you will put the bullet into the rifling lands, which increases pressure (the opposite of what you're trying to do), MIGHT set the bullet back deeper into the case when it chambers, so you lose that extra case volume you think you're getting anyway, AND if you get it inside a certain window, you can jam it into the lands, set the bullet back, AND hold the slide just ever so slightly out of battery, and KABOOM.
Determining your maximum OAL without rifling engagement, and basing a working OAL off of that, is a valuable step in reloading.
Let's assume that you've decided 1.12 is an all around effective OAL and look at an example:
Berry's 124gr HBRN. Bullet length = .616 That bullet will load to 1.220 in my CZ ShadowLine. That's the max without rifling engagement. So let's say you've decided that you're going to use an OAL of 1.12. Case length (.75) + bullet length (.616) - OAL (1.12) = seating depth (.246). And the jump distance is minus .100 out of the lands.
And...
BBI 125gr RN. Bullet length = .596. Max OAL without rifling engagement = 1.118. You decide to use an OAL of 1.12 because you like it. Case length (.75) + bullet length (.596) - OAL (1.12) = seating depth (.226). And the jump distance is plus .002 into rifling engagement (instead of out of it), worth a very slight increase in pressure than if you had been say minus .005 out of rifling engagement.
Montana Gold 124gr JHP. You believe bullets do better in your pistol at 1.12 in terms of accuracy, and you like loading long for the extra case volume, AND the professionally generated load data used 1.12 for its OAL, so you're going to use an OAL of 1.12. Here's the problem: Bullet length is .576. Maximum OAL without rifling engagement in my ShadowLine is 1.088. So case length (.75) + bullet length (.576) - OAL (1.12) = seating depth (.206). And jump distance to rifling is plus .032 INTO rifling engagement. And that is enough to jam the bullet good and hard into the rifling when it chambers, and it knocks the bullet back .015 into the case, so REALLY your seating depth is now .221 with your jump .017 into the rifling, with your bullet jammed good and hard into the rilfing, which will produce a pressure spike.
A little easier to see:
Berry Plated 124gr HBRN | OAL 1.12 | Seating Depth .246 | Jump .100 out of rifling
Black Bullets 125gr RN | OAL 1.12 | Seating Depth .226 | Jump .002 into rifling
Montana Gold 124gr JHP | OAL 1.12 | Seating Depth .221 | Jump .017 JAMMED into rifling
Same OAL all three loads.
The Black Bullets and Montana Gold have very close remaining case volume, with the Montana Gold having a little more, BUT the Montana Gold is jammed into the rifling and will operate at significantly higher pressure despite the extra case volume.
The Berry's HBRN is only .020 - .025 deeper into the case, but it has a jump of .100 out of the lands, which is FAR from the lands AND far from the other two bullets at the same OAL.
I know you weren't saying you should load all bullets at exactly 1.12, and that you might like to load the HBRN longer, but the point is that the two ballistically relevant numbers -- seating depth (which controls remaining case volume) and bullet jump can be dramatically different with two different bullets at
the same OAL. So it's not about finding the right OAL or OAL
range for your pistol. It's about finding the right OAL for a particular bullet in your pistol. And that OAL might be 1.060 or 1.100 or 1.120 or 1.165 or whatever, depending on the bullet. And the jump might be .005 or .080, you need to tune OAL for accuracy. Closest is not always best. And that process starts with determining your max OAL without rifling engagement, and working from there.
Make sense?
