08-14-2012, 08:27 PM
I'm late to the party, but I'll throw in my $0.02 having built a few lightweight ARs:
1. If you don't require a collapsible stock and insist on a polymer lower, then find a new or used Cav Arms Mk II lower as others have suggested. They have a solid track record.
2. Take a look at JP Rifles low mass operating system to mitigate felt recoil. I view the adjustable gas block, low mass bolt carrier and low mass buffer (if you use a rifle length receiver extension) as a system. They work well together that way. Together they permit you to build a lightweight weapon with just enough gas to cycle reliably with your preferred ammunition.
3. I like 9mm style upper receivers with no forward assist and no brass deflector. You can get 9mm uppers drilled for a gas tube from http://www.adcofirearms.com/
4. Last time I checked, Clark Custom Guns made the lightest forearm/free float tube--6 ounces in rifle length including the aluminum barrel nut. If you cut it to carbine length, it will weigh in right at 4 ounces.
5. I have a carbon wrapped barrel (an old ABS) and agree with other posters that you may be able to fine a conventional barrel (fluted or lightweight profile) with a lower overall weight. The CF barrels I've seen emphasized stiffness over weight reduction.
6. Don't underestimate the importance of balance. The AR I enjoy carrying and handling the most isn't the lightest one.
1. If you don't require a collapsible stock and insist on a polymer lower, then find a new or used Cav Arms Mk II lower as others have suggested. They have a solid track record.
2. Take a look at JP Rifles low mass operating system to mitigate felt recoil. I view the adjustable gas block, low mass bolt carrier and low mass buffer (if you use a rifle length receiver extension) as a system. They work well together that way. Together they permit you to build a lightweight weapon with just enough gas to cycle reliably with your preferred ammunition.
3. I like 9mm style upper receivers with no forward assist and no brass deflector. You can get 9mm uppers drilled for a gas tube from http://www.adcofirearms.com/
4. Last time I checked, Clark Custom Guns made the lightest forearm/free float tube--6 ounces in rifle length including the aluminum barrel nut. If you cut it to carbine length, it will weigh in right at 4 ounces.
5. I have a carbon wrapped barrel (an old ABS) and agree with other posters that you may be able to fine a conventional barrel (fluted or lightweight profile) with a lower overall weight. The CF barrels I've seen emphasized stiffness over weight reduction.
6. Don't underestimate the importance of balance. The AR I enjoy carrying and handling the most isn't the lightest one.