I see new handloaders especially, get all wrapped up in COL as if some Black Ops team was going to neutralize them if they get it wrong.
The length of a cartridge is determined by so many factors it boggles the mind. Well, mine anyway. For cast boolit loads I load my singleshot rifle's bullets to be as close to the rifling as I can get it. For jacketed loads, I try to get the bullet as close to .050 from the rifling as possible. That's what I try for. Reality sticks it's boogery nose in and makes my life all slimy. Some bullets are too short for this ideal and some are too long, compressing the powder too much. Bullet nose shape makes a big difference as well.
Then there are my magazine fed rifles where the big bugaboo is magazine length. I think most load manuals give lengths which will feed through most magazines or simply parrot lengths published by ammunition makers. Ammunition manufacturers determine cartridge length by worst case scenario. Their product must work perfectly in any gun chambered for their product. Even when some drooling mouth breather loads .303 Savages into his WWI souvinir Enfield. Hey, I watched him do it.
So, the length of a given cartridge is dependant on too many factors to list and you'll have to arrive at it yourself. As long as it chambers, the bullet doesn't fall out of the cartridge while it's in your pocket, and it feeds through the magazine, all while producing those all too common .323" fifty shot groups at 500 yards offhand, you have found the perfect C.O.L.
An example. I have a Ruger #1 in .308 Win. and a M1912/61 Chilean Mauser in 7.62 NATO. Cast loads using a Lyman 311299 loaded .005 off the lands in the Mauser will not chamber in the Ruger. The same bullet seated .005 off the lands of the Ruger in the otherwise most accurate loads will pattern 10" at 50 yds. Seating them back to .125" off the lands closes the group to a reliable 3". That load also is the most accurate in the Mauser where it is .250" from the lands. Yes, boys and girls a quarter of an inch. Ain't rifles fun, people?
To make a long story interminable, don't get too invested in C.O.L. Every load in every rifle is different. Keep careful records so you can easily duplicate a success. Or if someone tries to get you to load ammo for them, a failure. If you can load some dismally inaccurate ammo for someone, he won't be back.
Gerry N.