I've been toying with the idea of getting a lightweight upper, if not a new carbine entirely for some time. Right now funds won't allow it (Ammo is pretty expensive;) ) but I'd like to have a framework for what I'd want.
Here is what I was thinking of so far:
A1 upper receiver
1/7 14.5 pencil barrel with perm. Phantom
6 pos. M4 stock
CAR hand guards
Hogue grip
Side sling mount
BFG Vickers sling
This carbine would be a "survival tool" that could be used for extended periods of time without concern for damaging optics, replacing batteries, or anything beyond loading, aiming and squeezing the trigger. As such, I think it would only make sense to help it blend in a bit better with my area by using either OD furniture or by going the expensive way and doing a camo job.
Right now I don't have any bare-bones carbines, both are M4's, one has an Aimpoint, an MI rail system with the KAC covers and grip, and a BUIS. The other has a 13.2 LaRue rail (which I think would only lead to an inability to properly clean underneath the rail since I doubt I'd be packing a strap wrench everywhere) and MI front and rear BUIS's as well as an EOtech and KAC grip. Neither of these rifles is really lightweight, and I think the optics are nice but I can easily see them getting damaged or fractured to the point of no real use, other than occluding your irons.
That's what leads me to the A1 upper. Its simple, and can't be accidentally adjusted or messed up, plus its durable. Irons don't break or need batteries as well.
Finally, my reason for keeping it light is that in such a situation, I'd want a carbine that is least intrusive to my movement as possible. That means small, and light. Since I'm not willing to go NFA or contend myself to short range ammo effectiveness I'd go with 14.5 barrel with an effective FH for 16" overall.
What are your ideas and tips for lightweight carbines? (Not necessarily for "survival" uses.)

