I don't have one yet.
However, am looking real hard at the AAC Element:
http://www.advanced-armament.com/product.aspx?pid=488
Will also run with .22Mag and the .17HMR, 4.3oz. Don't think it will take the 5.7. However, since I'm not a 5.7 fan that's not an issue for me.
Tons of options out there, that is for sure!