I am starting another AR build but this time with the emphasis on making it as light weight as possible.  I had a couple of questions that I hope I could run by more experienced people

1.  Is there such a thing as a light weight upper?  If so, what brands come to mind.  As far as I can tell they are all about the same but can't figure out why there is such a huge price difference sometimes.

2.  I'm planning on using a Fortis Rev rail.  Is there any type of upper it will not attach to?

3. Finally, is it worth looking into a light weight BCG?  A lot of people say it messes up the timing but I wasn't sure. If it does, why would anyone run one?

Thanks in advance for any help.

1. I'd look into an upper without a shell deflector and/or forward assist. Rainier Arms comes to mind.

2. I THINK it won't work with some billet uppers, because of the anti-rotation tabs. But if you want lightweight, then you don't want billet anyway.

3. I would personally go with a normal BCG for simplicity. The light weight BCGs, JP for example, need a special buffer or spring (I may be wrong)

I'm unsure about your specific rail but all 99% of rails got into either the milspec barrel nut, or have their own barrel nut.  I've heard about carbon fiber rails, but I have no experiences with those. Some aluminum rails can get pretty light

I don't know of any specific uppers to be light weight (others can chime in for this.)

You can look into fluted barrels and different materials like stainless vs steel. However you want to take this into account of wat the rifle is being used for.
When I dd an SBR I took weight into account and wanted chrome lined with a 1:7 twist. I couldn't find anything at the length  and twist I wanted so I turned my own down. But finding a host barrel I got a government profile carbine and cut that down.

Also, I've never owned one, but you can look into pencil barrels.

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I wouldn't lighten up a bolt carrier group because there is a balance with the weight of it, the buffer, and the recoil. To little weight and your rifle won't have enough inertia to strip the next round . If yours is semi, a semi auto carrier is slightly lighter than a full. . If it's full auto, you don't want to use the lightest components as it will need to work with timing

A few companies make standard uppers without a forward assist. Tack that to a 14.5" pencil carbine barrel and use a standard BCG with it, and with the Fortis rail you should be plenty light.

Accessories are usually where the weight comes from. Run a micro red dot like an H1, a light weaponlight like an Inforce WML, and a lightweight stock like a CTR and you should be able to do everything anyone else can but be significantly lighter. Hell, I have a 15" rail but run about 2 pounds lighter than your average M4'gery.

Believe it or not, dumping the standard handguard and front sight base for a lightweight rail sysyem and low pro gas block is usually the easiest way to shed the pounds. It may only gain a quarter pound in reality, but muzzle end weight is where it makes the most difference.

I think it's not only the overall weight of a rifle it's where the weight is. The word fulcrum comes to mind, if you put weight at the end of the rifle it will feel heavier.

With that I suggest a short rail and a thin barrel. The rail length is also dependent on how you shoot it, if you use your hand at the end of the rail like I see many do now you need a long rail and maybe carbon fiber is something to look into more.

Most companies give the overall weight of the rail so you can compare.

To keep the weapon light that means keep the bolt on stuff like lights and stops off. Maybe use the Magpul sights that are polymer and a very small lightweight optic. The AR is as designed a light weight rifle. No need to deviate from that design in terms of the BCG and receivers. You can get one without the forward assist, I don't think you really need it in a non-combat weapon. In the early days they did not have one and even later I think the Air Force versions did not have one. The dust cover does keep dirt out of the receiver so I would keep that. Go with a 20 round Pmag or similar mag. The more ammo the heavier it is.

I see some very light weight carbon fiber handguards, I have no experience with them but they are lighter.

If you are familiar with fulcrum you would know it's like a see saw, the more weight you put on the end of the rifle will make it feel heavier and balance forward more. You can see it, it is obvious with shooters and ARs with all that stuff up there, it makes the rifle much harder to maneuver and can fatigue you faster. I do wonder if you can get too light and that becomes a factor with recoil and operation. A lighter weapon will have more felt recoil.

Uppers are usually aluminum (correct?) so they're /all/ basically lightweight.

The weight is in the barrel, and a little in the BCG.  Choose a short 14.5 pinned carbine gas or 16" pencil barrel in middy gas.  

Gas blocks and flash hiders are out towards the end, si any weight on those will be noticable.  Get a light flash hider (i.e not a vortex), and a light small gas block (fixed A2 if you need irons, micro gas block if you dont).  

I went from a RRA 16" heavyweight barrel with an A2 FSB and a magpul handguard to a BCM 16" lightweight barrel with a VTAC extreme 11" rail and I saved 1 1/2 lbs off the weight of the upper.

Thanks for all the info guys.  I really appreciate it.

My wife, due to medical issues, has limited upper body strength & mobility.  But after shooting my duty rifle, she fell in love with the AR & gave me permission to build 1 for her.  So I too am in the planning stages of putting together a lightweight carbine.

I'm glad to read the above posts, because that is pretty much what I have planned.

I've been looking at the pinned lightweight 14" uppers from BRAVO & I'm leaning toward a middy gas system.  I will likely put a small RDS on top.

It'll probably get me banned from here, but I'm going with the New Frontier polymer lower .  Since it will rarely be used, much less abused, I'm not concerned about the polymer.

I hadn't thought of trying a lighter BCG.  

Of course, being a girly gun, it's likely to end up some bright color of purple, but I'm also thinking about getting a 22 upper for it as well.

Keep us up on your progress;  I'd be interested in how it goes.