Lightweight, Reliable, Accurate AR15 build. Got it running and its a honey.

dcmdon

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Hi all.

So I recently decided to build a lightweight AR for the women in my life. Namely my wife and with a .22 kit my daughters. I'm kind of an accuracy freak so I wanted a decent barrel. Finally, I didn't want to spend a fortune on it. I didn't have a fixed budget but I wanted to restrain myself. Oh and one other thing. I didn't want to wait 6 months for some esoteric part designed to save me 3 ounces.

After all was said and done, the rifle ended up weighing in at 5.2 lbs with a heavy Miculek comp, M16 bolt, and an H Buffer. So as time passes, I'll be able to take a bit more weight out of it without undue expense once I can get my hand on a semi-auto bolt carrier, lightweight comp, and standard carbine buffer.

So here it is. I realize the look isn't for everyone. I think its cool.



The lower is a GWACS plastic lower.
The upper is just a standard A4 upper with the door left off. I tried to get my hands on a Les Baer upper without a forward assist but they aren't selling parts any more. As for a slick side upper, the DPMS one is actually heavier than a standard upper, and I also want a shell deflector because I'm left handed.

The handguard is a DPMS. I looked into Clarke's CF handguard and came to the conclusion that the only difference between it and the DPMS was the price.

The gas block is a JP rifles adjustable aluminum block that allows me to optimize the gas volume for the carbine length gas system. (This allows you to negate the advantage of a midlength gas system)

Finally, there's the Lothar Walthar 16" very light contour barrel barrel.

I' was shooting 2 MOA with a dot sight (rested) while breaking in the barrel. So far so good.

Don
 
Very cool!

I was at MFS recently, and one of the guys pulled an all polymer AR off the wall to show me. I was blown away at just how light it was. Upper and lower all polymer.

Felt like an airsoft rifle!
 
I only know of one non-metal upper, thats the Carbon 15/Bushmaster. It gets mixed reviews. Remember, all the "magic" happens in an AR upper. All the lower does is hold the fire control parts in proper alignment. I'm not yet ready to make the jump to a polymer upper.

You could probably save a pound off my gun by using a JP low mass operating system (+$400) and an ultra light weight 14.5" bbl with a fixed brake.

However neither of these met my original requirements.

The JP LMOS is a fantastic system, but its designed for competition guns that are kept very clean. The lighter BCG combined with an adjustible gas system allows you to put very little energy into the reciprocating parts of an AR. Good for shot recovery. Bad for reliability of the gun is dirty. There's simply less potential energy available to slam a round home if the gun is dirty.

The ultra light barrels are great. But I wanted to keep a standard .750 gas block so I could use the aluminum JP block. The Lothar Walther bbls are also quite a deal at an MSRP of $200. As anyone who has built anything knows, you make choices and compromises. Cost, availablity, accuracy, weight, reliability. They all pull in different directions. Even if you decide cost is no object and you are willing to wait for anything, weight, reliability, and accuracy work against each other.
 
I only know of one non-metal upper, thats the Carbon 15/Bushmaster. It gets mixed reviews. Remember, all the "magic" happens in an AR upper. All the lower does is hold the fire control parts in proper alignment. I'm not yet ready to make the jump to a polymer upper.

The poly lowers have been failing at the buffer tower bend, right smack dab in the middle of the rear take-down hole. The upper seems like mechanically it would hold up. The M4 feed ramps through to the locking lugs are all part of the barrel, so no issues there. I don't know how the barrel nut could receive the proper torque, given the receiving threads are polymer. Seems like that part would be easy to strip by accident reaching for that last 1/16" to get the gas tube to align.
 
The poly lowers that fail are the ones that are designed like the alloy lowers. You can't screw a buffer tube into a plastic lower and expect not to have problems. At least not with the materials that have been used so far. The CAV arms design integrates the grip and stock and buffer tube. There is no buffer tower bend, so it avoids that stress concentration. I've still got my reservations about the front take down pin holes, so we'll see how it goes.

Re plastic uppers. Have you ever taken a carbine course. A standard AR "poops" into the upper. I've had my AR so hot that I could not touch the bbl or upper with an ungloved hand without burning it. I'd be leery of anything plastic dealing with that heat coming off the bolt carrier.

Besides. This gun is a fun gun. If the plastic lower proves problematic, I'll just slap an alloy lower on it. I've got plenty.

Ive also got a pink plastic lower, where all of this stuff is ultimately going once I've proven to myself it works.
 
I'm leery of the design up above, for the same reason. If you draw a 45 degree line from where the web of your thumb would be to the rear take-down pin, that's the stress line that typically fails. at 45 degrees, half the compression force of the buffer moving rearward is transferred to that line, causing the fracture. It doesn't help this is also where the rear take-down detent hold is drilled, giving the stress fracture a place to start. Besides, if I have a decent stock, I'm going to beat someone to death with it.

Defense distributed I think has the right idea; add material and counter-sink for the pins and safety select to beef up that stress line.

I haven't taken a carbine class, but I did spend 5 years in the marines; does this count? I see your point about the heat, I'd like to take a torch to a poly lower and see at what point it begins to break down. That could actually be a fun bench test.

I'm a firm believer in the 80% lower angle and the NFA personally-crafted firearms. I think I would make many more (I've made 25 or so to date) of these before buying a polymer lower. But, I'd probably buy a polymer lower before the 3D printer to attempt to recreate Defense Distributed's work.
 
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If you were in the MC then you know a hell of a lot more than I do.

Remember though, the lower doesn't get nearly as hot as the upper. One other thing. Many of the injection molded AR lowers that have popped up lately were the result of shortages of proper forged lowers. This lower has been around for years and has a proven track record. Very simply, they do not have a reputation for breaking. I googled things like Cav Arms lower broken and fail and came up with very few hits. I got more hits under Cav arms 3 gun.

The defense distributed thing is an interesting exercise. Its useless in the US at its current level of sophistication.

There is no need for a liberator type pistol when you can so easily just buy a gun. Remember, in most of the country a secondary transaction involves nothing more than you giving the seller money and the seller giving you a gun. No paperwork. No paper trail. No record, its invisible. So no point in buying/making either a liberator or a firearm from an 80% lower unless you are doing it as an intellectual exercise. (which I totally get)

Where the Liberator is useful is in countries where Governments have made it virtually impossible for the public to defend themselves with firearms. But in the Good Old US of A, its irrelevant . . . for now.

Don
 
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