I'm looking for an AR 15 type much like Bushmaster m4 type that would double as a camp defense gun but also as a light weight predator or varmint type. I'm 66 and in good health but I want to avoid packing weight. All I can think of are the Bushmaster's that are 16" barrels and these are ready for a scope rail or iron sights. But these are 20". Their Predator Carbine is 8 pounds! Any ideas? Thanks.