Exactly. SOO if you reload, with a shorter barrel, you can optimize powder burn. The point you, and possibly the OP, are missing is the that a kettle is black. You can paint it, but its still a kettle. You can shoot a 308 at 800+ yards, you can also shoot a 22LR at 400+ yards, both of which I have done. You can shoot a 308 out of a 50" barrel with the slowest powder available, but its still a 308 and will be limitied by more than its case capacity. Its still not a porclein (sp?) bowl. The point is to optimize a cartridge for your use, and the 308 is not optimal for long range, but since you own a 338 LM, I feel you have grasped that concept.
If you want to discuss how you can engage a target at 1200+ lards with your 223/308 there are other forums more inclined towards sprayin/praying and non accurate rifles.
If you call a gun smith and ask for a custom build, he will ask what you want. If you ask a GREAT smith to build a custom rifle, he will ask what you want to use it for and build from there.
Again nothing wrong with a 308 as a rifle to learn the basics, but dont try to paint it porclein and call it a shitter...wait...what?!?!?! haha...
Regards,
DT