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Old September 6, 2010, 01:10 PM   #1
David the Gnome
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Ultra Lightweight AR-15 Build

Last year I purchased this CMMG carbine because I wanted an AR that I could add some accessories to. I put an EO Tech red dot on it and a vertical fore grip and it felt pretty good when I practiced bringing it up to the firing position at home. Here is a picture of it as I had it configured:



Fast forward to this Labor Day weekend; I went to an all-day tactical shoot with some friends and had to lug this thing around all day long. By the end of the day, all those accessories that seemed so cool at home made my carbine a lot heavier than it needed to be when it came time to actually use it.

So now I'm looking at lightening this carbine. The first thing I want to do is get rid of the quad-rail. I actually did a lot better without the fore grip so there's really no point in having that metal quad rail if I'm not going to hang anything off it. I was thinking about replacing it with a Magpul MOE hand guard, I liked the feel of it and it looks nice and light.

The butt stock isn't really very heavy at all but I was thinking of replacing it with the Magpul CTR stock, just to match with the hand guard more than anything. The weight gain/loss would be negligible compared to the factory M4 style butt stock.

I'm not sure what to do with the EO Tech. I really like having the red-dot but that thing adds a lot of weight on top of the rifle. I might be able to balance the rifle a little better by moving it back some more or something. I feel like it may be too far forward right now.

Other than those small changes, what would you suggest to help lighten this carbine a little more? I thought maybe a thinner barrel would shave off a decent amount of weight but I'm not too sure how involved that would be to replace/have replaced. I guess there's always the option of purchasing a polymer upper too. I'm also using polymer mags as another way to save some weight. I'm liking the 20 rounders but most of the courses are set up with a 30-round mag in mind, the 20-rounders require a few more reloads per run.

I guess there's always the option of selling this and buying a Bushmaster Carbon 15 or something too. I just hate to do that since I already have this AR.
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Last edited by David the Gnome; September 6, 2010 at 01:24 PM.
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Old September 6, 2010, 02:03 PM   #2
DnPRK
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DPMS is having a sale on lightweight carbine kits for Labor Day. If you want a lightweight carbine, this could be for you.
http://www.dpmsinc.com/store/?cat=1922

One addition I would make to the DPMS lightweight kit is the addition of a carbon fiber free float tube. It weighs less than 6 ounces and tightens groups from lightweight barrels.

Other weight reductions are an Ace lightweight stock and relacing the heavy steel front sight with an EGW aluminum gas block that is a third the weight of the steel front sight tower.

Last edited by DnPRK; September 6, 2010 at 02:08 PM.
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Old September 6, 2010, 02:38 PM   #3
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I say go for an aimpoint T-1 or Eotech XPS to reduce some weight. When I take my TA01/DOC off my rifle and put on my T-1, I feel an immediate and drastic reduction in weight. That aside, I just suck it up because I want a weapon-mounted light and VFG.
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Old September 6, 2010, 02:39 PM   #4
zoomie
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Ace UL stock, Aimpoint micro, carbon fiber handguard... That's all I can think of without going to lighter receivers.

Edit: Looks like I should have refreshed the thread before I posted as others said the same thing. Oh well.
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Old September 6, 2010, 02:54 PM   #5
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A little weight on all the parts adds up quick, but the only part you can save a lot of weight on is the barrel. What is the profile under the handguard?

I have an AR built on a Cavalry Arms Mk2 lower, with a Clark carbon fiber handguard, low profile gas block, 16" Ko-Tonics light weight barrel (similar to the old A1 profile), and a Weaver 1-3x20 scope. It tips the scales at just under 6 lbs.
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Old September 6, 2010, 03:39 PM   #6
Bartholomew Roberts
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The biggest place to save weight is the barrel. A lightweight barrel profile can shave almost a pound compared to the HBAR. Replace the quadrail with a Clark's custom tube. The Ace UL stock - all of that will trim the rifle down. If you want to get hardcore, you can go with carbon fiber uppers and lowers and a lightweight aluminium bolt carrier. These will be more finicky about the conditions they run in; but you can get pretty light. I've seen one AR that was less than 5lbs.
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Old September 6, 2010, 03:44 PM   #7
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Quickest route would be sending the upper off (I'd probably use ADCO gunsmithing for this) to have the barrel re-profiled to a lightweight profile, have a Daniel Defense Lite rail installed (if you want to keep quad rails), and chop it back to about 14.5" and have the flash hider permanently installed.

That's going to make it about as light as possible. If you want to save weight on the optics, I'd go with an Aimpoint Micro (LaRue has superlight mounts for them too... get a combo) or an EOTech XPS. You still want them mounted forward on the receiver; it preserves your field of view as best as possible.
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Old September 6, 2010, 03:46 PM   #8
David the Gnome
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The barrel is a 16" M4 contour barrel. How involved is replacing the barrel? Is it something I could do at home or is it something I'd have to send my upper off for? Would I perhaps do better just selling my upper and buying a lightweight upper that's already built?
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Old September 6, 2010, 05:04 PM   #9
Bartholomew Roberts
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Going from an M4 profile (assuming a true M4 profile, some companies have the M4 notch out front; but an HBAR profile under the handguards) to a lightweight 14.5" barrel will save you around 4 oz - not a lot of weight but removing it from in front of the barrel nut makes a big difference.
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Old September 6, 2010, 06:50 PM   #10
sonrider657
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Using a stripped Carbon-15 Upper, a Bushmaster super lightweight barrel, and a Cav Arms MkII lower, I built this 16" carbine at 5 lb. 1 oz. (without magazine). It handles and shoots great.

Cav Arms Lowers are no longer in production but DSG Arms has some for $89.00. Grab one while you can!

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Old September 7, 2010, 08:34 AM   #11
kymarkh
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Wish I'd have known you were looking at lightweight AR's when we met last month - I had my lightweight with me as I'd just sighted it in. It's not an ultra lightweight but it's pretty darn light for a 16 inch AR with optics.

It's a LW Bravo Company 16 inch midlength upper with standard handguards and an Aimpoint Micro. Right now I have the standard buttstock but I'm looking to go CTR also and will pick up the midlength MOE handguards when they are released. It's a little less than a pound lighter than my Bushmaster M4A3 with the carry handle mounted but you can easily notice the difference because the weight has been removed from the front of the gun. My only regret is that I didn't go 14.5 instead of 16 when I picked out the upper but I really like the midlength gas system and sight radius.

The ADCO route suggested is probably the quickest and cheapest way to go unless you want to purchase a new upper. Cutting it down to 14.5, turning the barrel down to a light weight profile and permanently attaching the flash hider would take off maybe 1/2 a pound out front where it's most noticeable.
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Old September 7, 2010, 11:14 AM   #12
gunmoney
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Not to be to rude here but toughen up chief. Maybe rather than rebuilding your rifle you should practice with the one you have a little more. Your quad rail maybe weighs a few more ounces than a MOE. Which style are you using with your vertical grip? A vertical or AFG can make a world of difference in control when shooting, but if you are just grabbing on to it like a pistol grip, it won't really help much. My objective in shooting may be different than yours but I am trying to be as effective as I can be. Being effective does not always equal comfort and the easiest path. That being said, I have no problem with lightweight carbines. But don't use it as crutch/excuse for your shooting either.

Last edited by gunmoney; September 7, 2010 at 12:13 PM.
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Old September 7, 2010, 11:36 AM   #13
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Not to be to rude here but toughen up chief.
I agree. There isn't even a Light on that weapon, and you're already willing to dump it for a plastic piece of junk AR???

C'MON, MAN!!!
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Old September 7, 2010, 01:04 PM   #14
Skans
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Just start out with an old Colt SP1 Carbine and replace the aluminum buttstock with one of those new lightweight plastic ones. Doesn't get much lighter than that. It's those heavy barrels that are adding all the weight. No need for those on a semi-auto .223.
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Old September 7, 2010, 01:20 PM   #15
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Not to be to rude here but toughen up chief.
+2

The .223 needs a heavier barrel due to it's high velocity and how it can heat up a barrel quickly. You might as well get an old series mini-14 if you want the lightweight barrel.
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Old September 7, 2010, 01:28 PM   #16
Skans
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The .223/5.56 in semi-auto does not need a heavier barrel. That's all a bunch of hype unless you're doing long distance bench-rest type shooting. And in that case, you'd probably choose a bolt action rifle. I used to shoot a Remington 700 .22-250. That's a high velocity round, and it did not require a heavy barrel to be extremely accurate.

If you think you need something with a heavier barrel, you might as well step up to a .308.
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Old September 7, 2010, 01:42 PM   #17
sonrider657
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Using a lightweight gun has nothing to do with lack of "toughness". Lightweight guns handle better and are easier to get on target, no matter how tough you are. Was Lance Armstrong a wuss for shaving every possible ounce off his bicycle? No, he realized that every ounce he saved was a competitive advantage. If you can get your gun trained on the bad guy quicker than he can get his on you, you win and live.
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Old September 7, 2010, 01:48 PM   #18
gunmoney
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The .223/5.56 in semi-auto does not need a heavier barrel. That's all a bunch of hype unless you're doing long distance bench-rest type shooting. And in that case, you'd probably choose a bolt action rifle. I used to shoot a Remington 700 .22-250. That's a high velocity round, and it did not require a heavy barrel to be extremely accurate.

If you think you need something with a heavier barrel, you might as well step up to a .308.
This is a common misconception Skans. Most modern AR type rifles have heavier barrels due to the fact that their perceived use involves a high or constant rate of fire. The rate of fire will cause the barrel to heat up quickly and cause the dreaded wondering point of impact from the barrel warping. A heavier barrels helps to combat that. A heavier barrel makes a rifle more precise due to the fact that it resists the warping from heat. A thin barrel can initially be very precise, but when the barrel heats up, it will warp, and the point of impact will begin to change. Velocity in itself is not the cause but the resulting heat from the high levels of friction. Again, this boils down to a shooter being able to rely on a more precise result to place his shot appropriately(Accurately). IF a thin, heat warped barrel can cause a huge unknown deviation from your point of aim to the resulting point of impact, it will not inspire much confidence in the shooter now will it?
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Old September 7, 2010, 02:30 PM   #19
Skans
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I'd like to see some real evidence on any AR barrel warping from semi-auto fire. I think it would take quite a bit of sustained full-auto fire to warp any AR15/M16 barrel.

I can't tell you how many rounds I've fired from my AC556 (mini-14) full-auto without warping it's "pencil" barrel. Then I'll take a few aimed shots after done playing and it's as accurate as it ever was (not a tack driver....but it never was - just consistantly accurate at 100-200 yards. No melting barrels, no warped barrel.

On an AK, I've loaded up 1 75 round drum and 2 30 round magazines, pulling the trigger as fast as I could going through 135 rounds as fast as I could pull the trigger (trying to get rid of some old Chinese corrosive ammo I didn't want anymore). I had to switch fingers, as they got sore, and my shoulder got pretty sore....Sure the gun got hot, oil on the barrel smoked, but the barrel was just fine - didn't warp, not even close.

Honestly, there is no need for heavy barrels or even fluted barrels on any semi-auto AR15. It's just for looks, that's all. Granted, some of the fancy fluted barrels do look pretty cool, though.

Last edited by Skans; September 7, 2010 at 02:49 PM.
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Old September 7, 2010, 02:36 PM   #20
gunmoney
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I'd like to see some real evidence on any AR barrel warping from semi-auto fire. I think it would take quite a bit of sustained full-auto fire to warp any AR15/M16 barrel.
Actually, so would I. It would definitely give a much better point of reference in approaching the choice of a barrel that will fill most shooting roles/uses.
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Old September 7, 2010, 02:59 PM   #21
Bartholomew Roberts
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The M4 barrel, M16A1 barrel and the M16A2 barrel all start with a 0.675" diameter profile that tapers until 0.625" underneath the handguard. On the M16A2 and M4 barrels, the barrel diameter increases to 0.750" at the end of the handguards and continues to the muzzle (with the exception of the M203 cuts on the M4 barrel).

Your typical lightweight barrel profile is 0.625" from the handguards to the muzzle.

By comparison, a typical heavy barrel profile for an AR starts out at 1.0" under the handguards and tapers down to 0.750" at the gas block. This is why a 16" HBAR profile barrel weighs as much as a 20" M16A2 profile barrel.

In terms of heat, on full auto, the M4 barrel (0.675-0.625 taper followed by 0.750") will fire approximately 500 rounds in 4 minutes before the barrel droops and bursts. The M4A1 barrel is 5oz heavier and starts out at slightly larger than 0.750" under the handguards tapering to 0.750" at the gas block (except for the M203 cuts). On full auto, it will do 900+ rounds continuously without bursting.

You can draw your own conclusions from all of that. The conclusion I drew is that if I was ever in a fight where the difference between a lightweight and HBAR barrel's ability to handle heat became a significant factor, I was doing much better than I expected in a fight I probably shouldn't have picked.
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Old September 7, 2010, 03:01 PM   #22
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When talking accuracy, people really need to be paying attention to the targets they expect to shoot and the distances at which they will be shooting them.

For a defensive carbine, it is not likely (not even remotely so) that you'll ever need to be taking shots out past 100 yards- there just aren't likely situations where someone at that distance is an active threat. Furthermore, the target is rather large. 3-4 MOA is just fine.

For this, a lightweight 14.5" barrel will more than cover you. You just won't be putting magazine after magazine through it at that distance. If you need the accuracy, your rate of fire will be slower, allowing the barrel to cool. If you're pulling the trigger as fast as you can, you aren't taking the time to aim very carefully, definitely not carefully enough for a 1 MOA capability to be realized.

A little realism is called for. Any event where extended range accuracy is needed, you'll be bringing the appropriate rifle. Any event where mobility is needed, ditto. You CAN have more than one, and no, you won't be having to make a hard choice of picking just one and heading for the hills.
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Old September 7, 2010, 04:03 PM   #23
gunmoney
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Maybe I am misunderstanding here. While I agree with what Techno and Bartholomew have said I think I was trying to point out something different. I am not worried about the barrel heating up and melting off of the gun. I am concerned with at which point a barrel (especially a thin barrel) heats up to the point that it begins to wonder. Now, at 100, 200, 300 yards, your dead bulls eye is now a complete miss, or you wound instead of kill, or hit someone or something standing right next to your target, or you are simply wasting ammo because you can hit nothing you are aiming at. Is it unlikely, maybe, but at what exact point does unlikely become possible?
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Old September 7, 2010, 05:56 PM   #24
Bartholomew Roberts
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I am concerned with at which point a barrel (especially a thin barrel) heats up to the point that it begins to wonder. Now, at 100, 200, 300 yards, your dead bulls eye is now a complete miss, or you wound instead of kill, or hit someone or something standing right next to your target, or you are simply wasting ammo because you can hit nothing you are aiming at. Is it unlikely, maybe, but at what exact point does unlikely become possible?
Whether the point of impact changes as the rifle heats up depends on a number of things, the quality of the barrel, how the barrel is bedded, etc. So the answer is going to be different for every individual rifle. The only way to find out is get out there with your rifle and shoot until you know at what point your groups start to open up due to heat.

However, the AR design is very good about maintaining accuracy as it heats up. Which leads to Technosavant's excellent point regarding evaluating your likely use. Let's say that after 120 rounds, the lightweight barrel shifts point of impact 2" up and 2" left at 100yds (hypothetical numbers). Now, how many defensive shooting situations are going to see you firing more than 120 rounds at 100yds? How often is that change in point of impact going to be an issue in your personal training or instruction? If you are firing at prairie dogs, then you may want a heavier barrel. Zombie apocalpyse? Heavier barrel may be in order; but even here you have guys going into heavy combat every day with the 0.675-0.625/0.750 profile barrels that aren't that far removed from the lightweight profiles. Even the SOCOM inspired M4A1 heavy barrel is a lighter profile than your typical commercial HBAR. I think that is a pretty good clue given the high volumes of fire those rifles see.
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Old September 7, 2010, 11:26 PM   #25
gunmoney
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Techno and Bartholomew, excellent points and information as usual. Skans, I appreciate your "edit" and the info you provided, it is good perspective.

I am trying to approach this in a scientific manner and in some way create or learn a gage that shows a cut off point, so to speak. (I think our discussion has gone a bit off topic) Anyway, for the average shooter, user, home defense, etc. the point is moot for their use, as you all have said. My mind is a bit more inquiring though and I like to know my firearms inside and out and their capabilities from one end of the spectrum to the other. If one of my carbines sh@#s the bed, so to speak, I want to know why or at least can start to recognize when it may occur. Just like a long range precision shooter should knows his rifles behavior at all stages and in all conditions I want to at least have a theoretical benchmark.

So apply that to this discussion. Scenario, If I took a lightweight, a govt profile, and a heavy Colt carbine barrels (16" or 14.5" M4 profile, either way) and did controlled tests with each, I would like to obtain at which point I should start to get nervous with each, if that point was reachable at all. AS far as most are concerned, a lightweight profile should suit most shooters. But I don't come here to argue "good enough". I want to discuss and learn. There are obviously all kinds of shooters, guns, qualities, configurations, calibers, ammunitions, and conditions related to this issue, so lets discuss them all.

The OP was honestly whining about not having fun shooting because his gun was too heavy. Instead of just practicing more and adjusting his style, he wanted completely rebuild his carbine as to guarantee that he will never have to be strained or uncomfortable while shooting ever again. One of his plans was to install a lightweight barrel. As many have said, for a shooter like this, he will never exceed the capabilities of that profile of barrel. My argument(besides the obvious) is that I would rather have the most capable and versatile barrel rather than just good enough for the average shooter. The geek in me wants to know when "good enough" falls flat and "unnecessary" becomes necessary, regardless of the fact that it is likely or not.

Sorry for the hazing OP but you can't always rely on gear to solve your problems. If I decide to go run five miles and by mile 2 I am puking my guts out and on the verge of a heart attack, obviously I made a seriously miscalculation in my planning at some point along the line. Rather than spending a fortune on new running gear, implanting a mechanical heart and lungs, and lobbying the local government to flatten and straighten all hills and roads in my area, I might want to just go out and practice a little first. Get a little advice, adjust my technique, and just keep at it and you will most likely be much better off.
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