How do I build the lightest possible AR-15?

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Cap'n Jack Burntbeard

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How do I build the lightest possible AR-15?

My basic constraints are:

No SBR
Caliber - 5.56 x 45, it makes more sense than 5.45, which I originally specified.
Flat top upper
No iron sights
Rifle length free float tube handguards, no rails

How do i make it happen?
 
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Start with a Bushmaster(or other mfg.) carbon fiber lower. That's where most of the weight savings can be had. Second get a smoothe upper receiver(no forward assist).
Next SBR it, whoops, lol!

But seriously, the first two options will save most if the weight, and using a railed gas block, and simple rear sight will finish it.

No expert here, but those are the mods I'd start looking for, and pricing, in an ultra light AR.

Someone will be along shortly to tell you to workout more:D...

Still 2 Many Choices!?
 
For starters, sounds like you want a Bushmaster Carbon 15 upper and lower receiver. Bushmaster doesn't make any uppers in 5.45, so you'll need to buy a bare upper and put everything together yourself, or have a gunsmith do it.

The rest is fairly easy. Mil-spec buffer tube is lighter that commercial, so go for that. Dunno what the lightest stock is, but that should be easy enough to find. Pencil barrel. Either a 16" post-ban style, or 14.5" or 14.7" with a permanently attached flash hider. Micro gas block. I believe free-float tubes are lighter than standard handguards, so then the lightest rifle length one of those you can get. That could be trickier, since there are so many AR-15 tubes available, but you can skip anything with rails, as those will usually be heavier.
 
shortest possible barrel in a light "pencil" profile will be the best way to cut weight. From there, there are lightweight stocks, lightweight/low-mass buffers, low-mass BCGs, and polymer and light-weight lower receivers to consider.

The problem though, is the cost. The lighter components are substantially more expensive.
 
I'm not too worried about the cost.
Enlighten me on these low mass BCGs and buffers, would that not affect reliable cycling?
If they don't, this is almost too good to be true.:cool:
 
http://www.bravocompanyusa.com/JP-Low-Mass-Stainless-Carrier-Assembly-w-QPQ-Fini-p/jpbc-3.htm

Very very interesting. My full-auto BCG is 11.5 ounces, in comparison (oh, wait, that's with the bolt in. 10 ounces with the key and firing pin.). And BCM is a great vendor. They tend to not carry anything that doesn't work.

The lack of forward assist serrations is perfect, since a Carbon 15 upper has no forward assist.

I think the absolute lightest possible lower would be a Cav Arms Mk.II (good luck finding one, though), with the lightweight buffer mentioned on BCM.
 
well, I imagine there wouldn't be a market for them if they did. Problem is, I don't know much about them either - just that they exist; i have no experience with them...

http://www.bravocompanyusa.com/JP-Low-Mass-Stainless-Carrier-Assembly-w-QPQ-Fini-p/jpbc-3.htm

http://www.bravocompanyusa.com/JP-Low-Mass-Rifle-Buffer-p/jplmb buffer.htm

a ~6oz. BCG and a 3oz. buffer, compared to what I say feels about 18-20 oz. of weight between a standard full-auto BCG and an H buffer.

Not only is it noticeably lighter, but it also helps with recoil by lowering reciprocating mass. Seems well worth the money. Lemme know how it works if you go with it, because this would be interesting to drop into a Del-Ton pencil kit with a lightweight full-sized stock.

The only problem is that they seem to only have a rifle-length buffer available. Not bad, since there are lightweight A2-sized stocks out there that make any carbine stock feel hefty, but that means that a lightweight A2 stock will also set you back a ways.
 
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The only problem is that they seem to only have a rifle-length buffer available. Not bad, since there are lightweight A2-sized stocks out there that make any carbine stock feel hefty, but that means that a lightweight A2 stock will also set you back a ways.
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Not a problem, I have an ACE ultra light on my LR-308 the stock weighs only 142g ( approximately 5 oz ) and they cost about $90.
 
then it sounds like you just might get an AR to weigh juuuuust under five pounds unloaded. :eek::cool:

I say go for it.
 
Oh and I hate rails, I hate them with a passion.
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You don't have to have rails on a free-float forend. Smooth ones, or ones with removable rails, can be had from several manufacturers. PRI comes to mind.

On a side note, most of the railed fore ends that are lighter than A2 HGs gain enough weight to make them heavier after you add rail covers - and keep in mind that rifle fore ends have a lot more rail to cover...

I have another question, what barrel twist rate is best for 5.45 out of a 16" bbl?
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I have no idea, but AFAIK the only companies that offer 5.45 bbls are Smith, M1S, and Oly. IIRC, they all have 1/8 twist.
 
The CavArms or Bushy Carbon lower, a Bushy Carbon or Les Bear non-forward assist upper, don't skimp of bolt carrier or buffer weight if you expect to shoot full power loads. There are some nice small gasblocks out there, I like the looks of the Badger. Check the weights of carbon fiber free-float tubes I don't think you will find a lighter setup unless you stick with old style CAR hand-guards. If I was to make one again I would choose a mid-length gas system. A SBR barrel with a perm attached flash suppresser is gonna weigh more than a plain 16.1" barrel.
Mine is on the CavArms lower with a lightened DPMS M4 barrel, less than 5.5 lbs with iron sights, big bonus is the weight balance is almost perfect, the CavArms lower is not easy to get balanced up with 20 inch barrels unless you put ballast near the buttplate.
 
Cav arms has very nice fixed stock polymer lowers. Very light. If you can get them..........

I wonder who will buy the Cav arms equipment and start making these lowers again?
 
Carbon Fiber have a rep for twisting/they are still working feeding bugs out of, don't they? I found just a pencil barrel and standard telescoping stock makes an incredibly light, balanced, handy arm.
Al
 
So the question is where do I get a pencil profile barrel in 5.45?
And where do I get a bare bushmaster carbon fiber upper and lower? Bushmaster seems to only sell complete carbon 15s.:banghead:
 
If flash and blast is what you want, just get a nice recessed crown and either enjoy the weight savings of put that weight to somewhere it will do you good, like a better optic.
 
Also, what is the lightest possible muzzle brake? I have no need for a flash hider since flash and blast is part of the fun.
Click to expand...

if you can't find a non-thread barrel, then buy whatever you can, take off the hider/brake, and put a simple muzzle nut/thread cover on it.
 
a muzzle brake is going to weigh more than a flash hider ever will. Do you know what a flash hider looks like? It's about the size of a baby carrot cut in half. We're talking extremely light weight. The A2 flash hider is mostly cut out anyways, so the material used is pretty minimal.
 
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