Let me start by saying this my favorite gun. Whats up with it feeling heavier than the SCAR? I am in no way advocating the SCAR , I will be buying the ACR but what is making it feel heavier?Other than that its the perfect gun.
The ACR is lil' heavier then the SCAR, by bout 12oz. However, the balance of the SCAR is just a wee bit mid magwell, where the ACR with folder fully extented and basic handguard is just forward of the magwell.
This is due to the heavier profile of the forward part of the barrel and beefier gas block. Personally It doesnt bother me. I own both and find myself using the ACR at the range more and more.
I thought the XCR was heavy when I first picked one up. You kind of get used to it but it all goes away when it's SBR'd so I've been spoiled. I think the ACR would be the same way. It doesn't account for much extra weight but why they went with an M4 contour still baffles me. (Fact: The only reason for the M4 profile is to mount an M203 and you can't mount an M203 in that manner to an ACR.)
You can shave some weight there by contouring the barrel as well as cutting and pinning your barrel back with a Phantom or other flash hider of your choice. The shoulder the gas block seats against has more material than is needed too. It's not much but little steps can add up to help the cause. And just like cjt said, the center of balance is the key factor.
My enhanced ACR---with full Magpul 30, EoTech and sling installed---balances just forwrd of the mag well, which is where I put my left hand when firing.
Perfect balance for me as it stands, but I would take a little heavier barrel, if one becomes available.
A bit of nose heavy is good for offhand shooting.