Shaving mass from an AR

[MachIVshooter]

In case anyone is curious, I discovered last week that taking a 16" M-4 profile barrel and turning it down to .600" from the gas block forward will cut 3.3 ounces off the snout of your rifle.

Today, I found that machining a 6 port compensator out of 6Al-4V ELI titanium to replace the steel A2 birdcage is worth another 1.1 ounces.

Lastly, it is amazing how much difference a quarter pound at the very front of the rifle makes in it's handling. The thing wasn't heavy to begin with at only 6.52 lbs unloaded, but at it's current 6.24 lbs, the balance is more rearward. It handles similarly to my 7.5" SBR, which is actually a heavier gun as it's set up, but the weight is not so far out.

Sorry, no before pics.

 

[Malamute]

I believe the early Colt CAR-15 carbines with the skinny barrels were either 5.5lbs or 5.8lbs empty.

 

[MachIVshooter]

I believe the early Colt CAR-15 carbines with the skinny barrels were either 5.5lbs or 5.8lbs empty.

Yep, and one can build a sub-4 lb SBR with what's available today, using magnesium or poly lowers, Al or Ti BCGs, hand guards like the BCM KMR, etc.

I just thought it interesting how markedly improved the handling of this specific rifle was by shaving a relatively small amount of weight and shifting the balance rearward. It also cost me virtually nothing to do, just ~$6 with of Ti stock. Guys have spent a lot of money cutting the same amount of weight in other ways.

 

[Arizona_Mike]

Yep, and one can build a sub-4 lb SBR with what's available today, using magnesium or poly lowers, Al or Ti BCGs, hand guards like the BCM KMR, etc.

I just thought it interesting how markedly improved the handling of this specific rifle was by shaving a relatively small amount of weight and shifting the balance rearward. It also cost me virtually nothing to do, just ~$6 with of Ti stock. Guys have spent a lot of money cutting the same amount of weight in other ways.

Sub 4lb is really hard. I hit 4.33lb with a 14.5" fluted pencil with no handguard cap shoulder, thin wall Manimal birdcage FS, magnesium upper, magnesium handguard, titanium BC, Cav15 lower/ stock. Ti safety, AL mag release, AL buffer retainer, and empty C buffer, Syrac gas LP block, AL dust cover door and rod, removed and plugged FA.

The only opportunity to go lighter would have been a conventional polymer lower and minimal stock, neither of which I trusted.

Mike

 

[HammsBeer]

What's the lightest you can get using standard aluminum receivers and a minimum 16" barrel length? This one is 6.5 lbs unloaded. I figured the only way to reduce weight any more while not affecting reliability would be a magnesium freefloat handguard, minimal buttstock, and replacing a bunch of small parts like the flash hider with titanium. Figure it could get shaved down to 6 lbs even?

 

[MachIVshooter]

What's the lightest you can get using standard aluminum receivers and a minimum 16" barrel length?

Depends on how much you want to spend. Ti or Al bolt carriers are significant, both in weight savings and price.

Going CF on the handguard will be the lightest, but if you want to stay with something modular, the BCM KMR is tough to beat.

Pencil barrels are obviously a must for LW builds.

I'd say 6 to 6-1/4 is about it without stepping into really high dollar LW parts. This rifle and another of mine are both at the 6-1/4 mark while staying under $1,000.

If your budget is high and you have the ability to lighten some parts yourself, you could hit right around 5 lbs with conventional 7075 receiver halves. But that's gonna require replacing just about every possible steel part with Al or Ti, and making lightening cuts wherever possible.

 

[AlexanderA]

When it comes to actual shooting, weight -- especially weight at the front end of the rifle -- is your friend. It lessens recoil, minimizes muzzle rise, and helps keep you on target. A heavy barrel also handles heat better.

Light weight is a consideration if you have to carry the rifle for extended periods. It would therefore be desirable in a hunting rifle, but not in a target rifle.

 

[rbernie]

Interesting - thanks. I like the looks of the comp.

Truth be told, I've found that I really don't like a strong rearward weight bias for a rifle that'll be shot offhand. In fact, I tend to work on getting as much mass off the back as I can, to make the rifle balance on/just forward of the delta ring/receiver ring. A light front end feels fast in coming up, but it doesn't 'settle' well for me in fast offhand work.

 

[Inebriated]

I've wanted to do a lightweight build around BCM's ELW-F barrels. Their 16" mid-length version is 21.5oz. No shoulder for the handguard cap, fluted, continuous taper... Seems like a great way to cut the weight without cutting performance.

I have the build outlined somewhere, IIRC it came to 6 pounds flat, with a light, and without sacrificing ergonomics.

 

[MachIVshooter]

When it comes to actual shooting, weight -- especially weight at the front end of the rifle -- is your friend. It lessens recoil, minimizes muzzle rise, and helps keep you on target. A heavy barrel also handles heat better.

That depends entirely on what you're doing with the weapon. As well, compensators accomplish the same thing that weight does, but without the weight

Not like 5.56 ARs really have much recoil or muzzle rise to deal with anyway.

If you're doing dynamic shooting, the lighter weight and more rear biased guns not only swing faster, but also cause less fatigue. That really matters when you're having to support the rifle.

Bench work? Yeah, go heavy. My 22" bull AR weighs in at 15 lbs, and barely moves when fired. But one 30 round mag in slowfire offhand, your support arm is about toast.

This rifle in particular is my wife's. She is 5'6", 118 lbs-pretty slight build. I'm 5'10 185 and fit, so a rifle that feels handy to me can be an anchor to her. I have no problem slinging around 10-12 lb 7.62 battle rifles all afternoon, but she's done with them before finishing out a magazine, and it ain't the recoil.

 

[rbernie]

If you're doing dynamic shooting, the lighter weight and more rear biased guns not only swing faster, but also cause less fatigue. That really matters when you're having to support the rifle.

I've carried an AR pattern rifle in the field from sunup to sundown, for many years. That means 'carry a lot, shoot once or twice'. I don't do much 'all day' work on a square range.

For a field rifle that depends on first-shot snap shooting accuracy and speed, my experience (and some modest work with a shot timer) tells me that rifle with a light front end is faster up, slower to settle, and harder on running targets.

But I still like your comp.

 

[MachIVshooter]

I've carried an AR pattern rifle in the field from sunup to sundown, for many years. For a rifle that'll depends on first-shot snap shooting accuracy and speed, my experience (and some modest work with a shot timer) tells me that front light is faster up, slower to settle, and harder on running targets.

Much like shotgunning. I like a 28" barrel for trap, and for pheasants or geese. But for dove or upland birds, where the animals tend to be close in and fast, being able to get on target quickly is more important than the follow-through. Thus I use a BPS-10 on pheasants and geese, but prefer my 24" Ithaca featherlight 20 for upland birds.

Similarly, for the informal carbine matches we do, the furthest targets are 50 yards, with a lot of closer in shooting on multiple targets, and moving part of the drill. When your accuracy requirement is 10 MOA + but speed must be high, the faster handling lightweight rifles rule the day. I can absolutely dominate those games with my 7.5" SBR, but that rifle is nowhere near as useful in 100 yard offhand shooting as my much heavier 16" Armalite M15A2C, even though the mechanical accuracy of the two is pretty close from a rest.

But I still like your comp.

Thanks!

 

[DavidMS]

I am trying to build a somewhat lighter AR15 and appreciate your suggestion to spend the extra money and get a lightweight muzzle device. Have you looked into carbon fiber forearms? I know they are expensive but seem to make a real difference. Is carbon fiber sufficiently durable to not make the rifle a safe queen?

 

[MachIVshooter]

I am trying to build a somewhat lighter AR15 and appreciate your suggestion to spend the extra money and get a lightweight muzzle device.

You don't have to spend a lot; there are some pretty reasonable mini comps and flash hiders.

Of course, this one cost me less out of pocket than a birdcage; about $7 worth of Ti stock. Could've used aluminum for even lower cost and slightly less weight, but I just wanted to play with Ti

Have you looked into carbon fiber forearms? I know they are expensive but seem to make a real difference. Is carbon fiber sufficiently durable to not make the rifle a safe queen?

I've not personally run any of them, but CF is pretty tough stuff. I have built RC car chassis and parts with it, and in many applications, it is superior to aluminum in strength. This 4mm thick CF chassis I built for my vintage RC10CE has taken some really, really had hits with zero damage-hits that have taco'd 3mm 6061-T6 chassis:



4mm was totally overkill in this application, and actually made the thing so rigid that it thing began shearing off screws on impacts. I had to make a pretty substantial 7075-T6 brace to mitigate that problem:



The thing to keep in mind about CF is that it is like wood; once you exceed it's limits, it snaps and splinters instead of bending. If, for example, you ran over your rifle, an aluminum handguard will probably be damaged significantly but still functional. CF tube, on the other hand, would split, and even if you could still grasp it, you wouldn't want to.

 

[Arizona_Mike]

When you take into account the barrel nut and attachment hardware, the new Magnesium alloy hand guards from Bravo Company are about the same overall weight as a carbon fiber solution.

Mike

 

[MachIVshooter]

When you take into account the barrel nut and attachment hardware, the new Magnesium alloy hand guards from Bravo Company are about the same overall weight as a carbon fiber solution.

That is true. At 6-1/2 ounces with barrel nut, the 10" KMR is dang light.

I could drop another couple ounces off that with a custom CF using an aluminum barrel nut and thinner material, but I don't think any production CF handguards actually come in lighter than the KMR for a given length.

 

[Baldman]

A carbon fiber wrapped barrel might help as well but the price miight be restrictive


http://proofresearch.com/the-products/barrels/ar-carbon-fiber-barrel-calibers-lengths/

 

[Arizona_Mike]

A carbon fiber wrapped barrel might help as well but the price miight be restrictive


http://proofresearch.com/the-products/barrels/ar-carbon-fiber-barrel-calibers-lengths/

At that price you'd think they would publish weights.

Mike

 

[MachIVshooter]

A carbon fiber wrapped barrel might help as well but the price miight be restrictive

If you want near HBAR or bull rigidity with light profile weight, yes. But if just trying to go as light as possible, the ULW/pencil barrels will be lighter. Every CF or fiberglass wrapped AR barrel I've ever heard of are really nothing more than a wrapped pencil barrel, since pencil is really about the minimum amount of steel.

 

[Blade First]

"Pencil barrels are obviously a must for LW builds." - Mach

Agreed. I'm always chasing a lighter build and my latest barrel acquisition weighs just 19.2 oz. It's an FN MG barrel, 16", turned down to .500" except for the step up at the gas block journal which is .625". Can't really justify chasing lightweight BCGs yet since the lower was somewhat pricey. Complete upper including flash hider and Samson 12" free-float tube is 3 lbs. 6.2 oz. No optic mounted yet.

Good news, however, is that the complete MAG lower is just 1lb. 13.8 oz. using the MAG 6-position stock. Saved a full .5 oz. by doing a grip reduction on the standard A2 plastic.

Complete upper and lower as spec'd above = 84 oz. = 5.25 lbs.

Figure at least another 1/2 lb. subtracted with appropriate funds applied.

Haven't shot it yet but looks like the weather will cooperate next week.

 

[zoom6zoom]

There are a number of makers who have created skeletonized receivers for the AR. The first ones I saw were for states that require pistols to be under a certain weight.

http://www.recoilweb.com/x-products-ultimate-skeletonized-ar15-38529.html