Optimal COAL

[J-cat]

Are you aware that there are a myriad of 9mm platforms with different chambers that don’t care what’s written in a manual? A manual contains information for a set of components that were fired in a test gun. Deviating outside those parameters is what we do every day because 1. we don’t have that test gun, and 2. we aren’t using those components. The minimum coal IS arbitrary in the context of the OP’s problem. One can certainly go below the minimum coal published in a manual or beyond the maximum if a proper load work up is done. As the OP so eloquently put it:

“The exact data for every combination of bullet and powder realistically doesn't exist.”

[sofbak]

I can't fix stupid.

I have little tolerance for the ignorant.

If you think that coloring outside the limit lines of published load data is an OK thing to do-then by all means go right ahead.

IDC

[J-cat]

I can't fix stupid.

But your local healthcare agency can. There you have access to mental health professionals who will fix you right up.

[sofbak]

^^^please feel free to do as your intelligence/education and experience guide you.

[Sandspider500]

[noylj]

CARTRIDGE OVERALL LENGTH is the distance from the bullet meplat to the case head. Nothing to do with trimming.
Next, forget ever hearing about trimming pistol cases and never contemplate doing so. A cartridge that headspace on the case mouth requires to longest case that fits the chamber (i.e., the case length should match the head space of the barrel's chamber). Taking a case that is already suffering "excessive head space" and trimming it only ruins what accuracy that case may have had.
Optimum COL: That distance from bullet ogive to lede/rifling that produces the best accuracy.
For most guns, this will range from the bullet just contacting the lede to being no more than 0.020" from the lede and the reloader must determine this for themselves.
I find that since all "head space on case mouth" cartridges are already starting with excess head space, that the bullet being as close as possible to the lede, without jamming the bullet in the lede is best.
In general:
Per Ramshot (and all other reloading suppliers):
“SPECIAL NOTE ON CARTRIDGE OVERALL LENGTH (COL)
It is important to note that the SAAMI COL values are for the firearms and ammunition manufacturers industry and must be seen as a guideline only.
The individual reloader is free to adjust this dimension to suit their particular firearm-component-weapon combination.
This parameter is determined by various dimensions such as
1) magazine length (space),
2) freebore-lead dimensions of the barrel,
3) ogive or profile of the projectile and
4) position of cannelure or crimp groove.

Your COL (OAL) is determined by your barrel and your gun and your magazine and the specific bullet you are using.
What worked in a pressure barrel or in my gun has very little to do with what will work in your gun. Load a couple of dummy rounds (no powder and no primer) to the max. COL (OAL) and see if it fits your magazine, feeds in your gun, and chambers in your barrel.
Seat the bullet slightly deeper until you achieve all three of these goals. This is the COL (OAL) for you in your gun with that make of bullet.

[Donny1]

What I'm learning is that the distance to the leade doesn't really apply to loading for a semi auto pistol. Considering different bullet profiles (ogive) variations vary, some bullets at the max COAL spec will be as much as .060 of more away form the leade. My Ruger PCC with Xtreme 124gn CPRN is 1.200 to the leade so at max, 1.169 is .031 away and I'm loading it at 1.130 to get the appropriate chono numbers and reliability.

Years in to this but still learning the basics.

[J-cat]

It doesn’t really apply until it does. There are some pistols where you have to seat the bullets real deep because they won’t chamber otherwise due to the short freebore. Also, in a 9mm carbine, playing with the coal can and will affect accuracy. I have cut groups in half with seating depth adjustment in my 9mm carbine. It’s worthwhile to try.

[Donny1]

Not sure how I would judge accuracy with the PC9 just yet because I still just have the irons but I can hit clay pigeons at 100 yards better than with the AR with a Red Dot (not magnified) free standing. That may be the trigger on the AR though, it's a bit heavy.

Curious on your COAL though, are you getting a benefit going longer/shorter?

[hermosabeach]

I have not found coal to be a big deal with my handgun loads

For rifles, you can play with coal to figure out how your chamber is cut, how long the throat is and what works best in that one specific rifle.

With pistols, crimp seems to make more of an issue.

If you shoot longer range where a bullet slows from super sonic to sub sonic before it hits the target, one can play with velocity to possible keep the bullet supersonic from the gun to the target or subsonic all the way.

[J-cat]

Not sure how I would judge accuracy with the PC9 just yet because I still just have the irons but I can hit clay pigeons at 100 yards better than with the AR with a Red Dot (not magnified) free standing. That may be the trigger on the AR though, it's a bit heavy.

Curious on your COAL though, are you getting a benefit going longer/shorter?