I think you are trying to transfer "off the lands" reloading practice for bottle neck rifle cartridges for straight wall 9mm reloading (Well, 9mm is "technically" a tapered case ... but more on this later) and there are some differences to produce finished rounds that will actually fully chamber reliably from the magazine and to produce greater accuracy rounds.
Load development steps are: Determining the Max OAL, then Working OAL and incrementally seating the bullet deeper to increase neck tension to reduce group size.
With bottle neck rifle cartridges operating at much higher chamber pressures than 9mm,
case "grows" longer as case base wall "thins" from pressure pushing on the bottle neck portion of the case with subsequent reloading and eventually will require trimming the case neck or discard the case when case base wall thining is too much to safely contain the chamber pressure (Incipient case head failure).
Although 9mm is a "higher pressure" cartridge than say 45ACP, it is a "straight wall" case (Well, technically a "tapered case") and like most other
straight wall semi-auto case, case length actually grows shorter with subsequent reloading.
Why?
Because most resizing dies' carbide sizer rings do not resize all the way down to case base. With each firing and resizing of case, downward force on the case neck will gradually push brass/metal towards case base that continues to very gradually expand but since sizer ring do not reduce this portion of case, over time case will grow shorter.
Step 1 - Maximum OAL/COL:
9mm and other "straight wall" semi-auto cases headspace off the case mouth meaning during "clunk" test (Actually called
the "plunk" test due to "plonk" noise the round makes when dropped in the barrel), case mouth drops down and contact the chamber to make the "plonk" sound. And when we determine the "
Maximum" OAL, we identify the OAL that will allow the finished rounds to drop in the chamber freely with a "plonk" and spin freely without contacting the start of rifling for that particular bullet ogive and barrel combination.
BUT, what happens when you load to Max OAL with a shorter case? More bullet nose protrudes above the case mouth. And when you perform the barrel test, more bullet nose (ogive) sticking above case mouth will contact the start of rifling. So
when I am determining Max OAL, I will measure samples of resized case length and use shorter cases as longer cases will allow less bullet nose to stick above the case mouth.
Step 2 - Working OAL/COL:
Depending on bullet nose profile (ogive)/barrel/magazine/pistol, rounds loaded to Max OAL can reliably feed from the magazine in some cases but usually, Working OAL is shorter.
To determine the Working OAL, we load dummy rounds (no powder, no primer) and feed them from magazine and release the slide without riding it. If dummy rounds feed reliably, this is your Working OAL. If not, I incrementally reduce the OAL by .005" until it does.
Step 3 - Powder work up and accuracy trending:
If you can find the same bullet/powder/primer published load data, you can use the same start/max charges. But if you cannot find the published load data for same bullet/powder/primer combination, I reference all available load data and use the most conservative start/max charges for my initial powder work up (As you can always go higher). If I can't find load data for the particular bullet weight, I will reference load data for bullet weight that is slightly heavier.
And if my Working OAL is significantly shorter than published (Let's say more than .010"), I will compensate by reducing my start/max charges by .2-.3 gr (As you can always go higher).
During initial powder work up range test, I will first identify the powder charge that will reliably cycle the slide and extract/eject spent cases then I will monitor accuracy trends to identify charge that will produce smaller groups. (If start charges reliably cycle the slide/extract/eject spent case while producing accuracy, often with faster burning powders, I will "Work Down" from start charge in .1-.2 gr increment to identify lighter target loads)
If I am pursuing greater accuracy (Say to develop match loads) and using mixed range brass, I will sort by same headstamp case and maybe same resized case length and test for neck tension and perhaps thicker case wall brass to eliminate bullet setback during chambering -
https://www.thehighroad.org/index.p...neck-tension-and-bullet-setback.830072/page-4
Why?
Even though you may produce consistent OAL with .001" variance, if you experience bullet setback during round chambering, your "Chambered OAL" will vary with different bullet seating depth to produce different chamber pressures that could translate to greater muzzle velocity variance (SD numbers) and increase scatter of groups size on target.
And with "no bullet setback" rounds, if I am not at max published load data, I will test for accuracy of group size by incrementally decreasing the OAL (Say by .005") to see if group size gets smaller. If yes, I will use shorter OAL. If no, I will use longer OAL. (I have done enough tests to show that compared to longer 1.150" OAL used for most 115/124 gr FMJ/RN bullets, shorter 1.130"-1.135" OAL produced greater accuracy from greater neck tension. And for 115 gr FMJ/RN with shorter bullet base sized .355", I used even shorter 1.115" OAL to produce greater accuracy)
Of course, since you are using HP bullet with longer base and shorter nose than FMJ/RN, your Max/Working OALs will be shorter around 1.045" - 1.120", depending on the barrel's leade length/start of rifling angle.
These steps are outlined in the 9mm load development -
https://www.thehighroad.org/index.p...-and-discussions.778197/page-10#post-11419509
I hope this helped.