I have loaded the 124 ball/fmj or plated from 1.14 to 1.12" OAL
for top FPS in my 9mm pistols , from a 3" to a 5" barrel.

Unique and bulky powders need the 1.14" due to their bulk but
I can use the 1.12" for powders like w231, CFE and BE86 that are fine grained.

I don't know what OAL to put down as my final over all OAL to use for all my loads
so I don't have to keep adjusting my dies.

What is your best length in your 9mm loads?

I haven't loaded any FMJ/ ball in the 9mm in about thirty years as I use only cast bullets. However, according to my notes, I used to load both 115 gr. and 124 gr. Winchester ball to 1.16", just under maximum recommended length. This OAL worked fine in several pistols. Other bullet makes may vary slightly in shape and length, but the 1.16" OAL would still be appropriate for most guns and magazines.

I don't think I own a 9mm pistol where that 2/100th of an inch difference in the OAL makes any difference with any RN, TC plated or fmj bullet of 115 or 124gr... Purely from a function standpoint.

How much powder can one put in that additional 2/100th of an inch?

The Hornady micrometer attachment for their Custom Grade seater dies makes fine OAL adjustments pretty easy.

Cheers!

P.S. I use 4.6gr BULLSEYE for almost all my 115 & 124gr 9mm loads. Flat nosed bullets (or HPs) loaded shorter, with RNs (especially 147gr) loaded longer. I don't see how one can "standardize" the OAL while using different powders, bullet designs and weights.

I start my bullets at mag length. Then do a "plunk" test in the barrel. If whatever bullet I'm loading doesn't hit rifling I go with it. Make sure there's enough bullet in the case, give it a slight taper crimp. Loaded some 124's today for a Glock that didn't hit rifling stacked in the mag that were 1.170 OAL. the deeper you seat them the higher the pressure.

I seat my 124JHP at 1.09", my 147JHP at 1.14"

What Luke Duke said!

Given the many bullet profiles in the same weight, small variations in chamber dimensions, and magazine differences, this is how to best determine the optimum over all length for your pistol. But as he has said, reducing the internal volume by deeper seating will rapidly increase pressure so be careful if you go to shorter than book OAL.

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SWCA #3526

The col is bullet and gun independent, and there is no "best" standard. You need to consider not jamming the bullet into the rifling, whether the bullet reliably feeds from the mag and pressure. Would not recommend using col just for purposes of getting max pressure from a specific powder, although recognising some bullet powder combinations will reduce your velocity potential. A specific example would be the older style sierra 9mm bullets.

Best to use your chamber to determine Maximum OAL for your gun(s). Some years ago I loaded 500 rounds to some OAL taken from a manual, and found they would not chamber completely in one of my barrels. I had to readjust the seating die and re-seat every bullet deeper so they chambered fully. Bullet profiles can make a big difference. The other consideration is keeping the OAL a little shorter than what will fit into the magazine. If it chambers fully and fits in your magazine, stop right there. Worrying about a “correct” OAL is nonsense.

That "best" seating depth depends upon bullet shape. A truncated cone/flat point bullet might have the same effective ogive of a RN but they'll have different OALs. They'll also take up a smidgen more space in the case. Your choice of seating plug shape can also make a difference giving different OALs for different designs.

I noted earlier that I pretty much standardized on 1.090 in as OAL with a couple of different bullet designs with pretty close to the same effective ogive.

You could always splurge and buy an extra seating die. Wish I'd have thought of this way back when. I quit buying RN 9 bullets and went to TC so I didn't have to fiddle with die adjustments. Long before that I broke down and did this so I didn't have to fiddle with my rifle seating die when changing from hunting to target loads. Did the same for one specific .223 bullet when someone was having a clearance sale.

I've been using Delta Precision bullets of late. They seem very consistent. Their 147 gr I can set out to 1.195 in a Glock Gen 5 9mm barrel, but have to seat to1.165 to work in my mag. But, that's my Gen 5 not the next guys his could totally be different I like the fact that I can set out farther because I can cautiously work up to max more comfortably. I really like 147's for a 9mm.
What was a recent discussion here " don't use others reloads" !