The lighter of my two AR10's is a touch over 40", with the adjustable stock at a normal shooting position. That's with an 18" barrel and a fairly long Vortex flash hider. You could save another 2-3 inches with a 16" barrel and standard flash hider. But it will be loud, and heavy (~10 lbs empty)
Mine does shoot decently, even on a windy day:
For a shorter, lighter gun, you may well want an AR in either .223, or .300 Blackout, which is sort of a .30 carbine on steroids