we get faxon barrels from brownells.no
the sphur/zeiss combo is 918 grams, vs 620 grams for the jp mount with swaro z6i, but its a very nice optic.. so probably worth the grams.
the handguard, barrel and upper can save you easy grams, slickside aero upper is 180 grams, faxon gunner light is also only 6-700 grams, also a nice light jp bcg saves quite a few grams, complete is only 250 grams, vs vooodoo which is supposed to be light, but is.. 280 grams. I assume you allready run a light buffer, think mine is like 50 grams? lighest jp, without the internal weights.
(I have all the faxon barrels and jp and others so I know)
the faxon handguard, is a lancer systems CF guard, with another mounting system, which actually makes it lighter than the original lancer system, which is good. BUT a toni systems handguard is just as light, or lighter (and way cheaper) also way more available here, others to look at is the.. err something something ultra lite with m look. but I prefer the toni.
With all this said, I dont feel weight limits is a that big issue, even my mini rifle setup runs a pretty heavy 20" setup.