assuming you are talkin about the M24 that the Army uses, it was due to giving them the option of changing to a 300WM, but in short if you are building a purpose 308 LA, yes it would be utilizing the ability to run a longer COAL
I have a long action that Randy just screwed on a 20" .308 take off for me. He pushed it back a bit. I can now load a 208 amax .01 off the lands at 2.99 inches.
And I can mag feed. I'll be able to see how it shoots this week.
Or use a Tube Gun Chasis from Competition Shooting Stuff (Gary Eliseo). Can't remember how many rounds in his mags, but played with one at ASC-Fall and it's sweet on a long action.