I have a LR308 with a 24 inch bull barrel that has shown to be very accurate and even heavier.  I am considering have it cut to 18-20 inches and reprofiled to a lighter weight.  

Uses are stand hunting and range fun to 500y both suppressed/unsuppressed.

Questions are:

If it cut it to 18, will the current gas port still suffice, and if not, what size?

What profile, specifically, do you feel gives the best compromise between stiffness and light(er) weight? As a comparison, the M110 AMU profile  is .875 GB and .850 muzzle, which is likely heavier than I am interested in.  Basically, I want it as light as possible while not giving up much in sustained accuracy.

Thanks in advance.

Why not just get the barrel fluted?

Why not just get a new barrel that meets your new needs? Keep the old one for that far off day when you regret irreversibly machining it down and wish you still had it. That day when you no longer climb up into stands or decide you are bored with 500 yards and want to go twice as far.

How much will all tha gunsmithing cost versus a new barrel. And with a new barrel you avoid the risk ruining the whole thing, should the smithing go south.

Who takes a long haul comfortable road car and tries to turn it into something it just isn't?

For the money you will spend, I would just get a new barrel from Fulton.

Been there though with re-profiling LR-308 bull barrels.

I think they rely on the weight of these barrels to compensate for the economy line of steel they source en mass.

Once you profile them down, they can be floppy.

An LR-308 24" bull is heavier than a SAKO TRG in .338 LM, for those that are wondering about a weight reference.