If so please post specs.
Cheers,
Mr. Smiles
Bushmaster’s carbon15 weighs in at 5.77 lbs without magazine. With a pencil barrel it might be in the 4s
Lightest ones I have seen and would still trust have been around 6lbs give or take. I would be doubtful if you could get one into the 4’s without some serious sacrifice.
My 6920 weights less than that, It has to be possible to get one at least around 4.5lbs, of course an sbr with a 7" barrel would be easier 
You might find the discussion in this thread of interest…
Even better than mine is Robb’s personal build: Project Featherweight
He got his down to 5.43lbs
Just to get into the 4 range you’d have to chop off a significant amount of the barrel. I can’t imagine how you’d get under four while maintaining a functional/reliable platform.
Cheers, Interesting stuff. Looking over it all now.