Weight of AR vs Bolt

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Krones

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Hi all,

I had a theoretical question that has bugging me lately. Why is an AR-15 about the same weight as a comparable bolt action rifle, and not heavier? ARs are made mostly out of metal and have a lot of extra parts (mag well, gas system, recoil springs, hand guards)... which all add weight.

Take for example the Ruger American Ranch: bolt gun fires 556 out of an AR magazine, has a polymer stock and a normal barrel and weighs 6.1lbs. Tikka T3X in 223 is not far off.
Then the AR556: same caliber, same manufacturer, 6.5lbs. SAINT from Springfield not far off.

Thanks!
 
The upper receiver, lower receiver, charging handle, and forearm on most newer AR are aluminum, as is the buffer tube. The barrel, bolt, and bolt carrier are of course, steel, as are the fire control group parts and various springs, pins and detents. The stock furniture and handgrip are plastic (or rubber). Of course they are going to be light.
 
Thank you for the responses, it makes total sense.
Why is aluminum not mainstream for bolt guns, especially in smaller calibers like 223?
 
AR bolt lugs lock into the barrel extension so the upper receiver doesn't really need to be steel as it mainly just contains the reciprocating bolt and hold the barrel in place. With most bolt action rifles the bolt lugs lock into the upper receiver itself so it needs to be hardened steel.
 
Consider the same question from the opposite approach - why are bolt guns as heavy as an AR? Then the answer to both questions becomes clear.

The steel receiver, bolt, and bolt handle are contributors to weight of a bolt gun which are analogous to lighter aluminum parts in the AR. The Seekins Havak Element uses a steel breech plug in an aluminum receiver, similar to the AR barrel extension, and uses a steel bolt head carried in an aluminum bolt body. It uses a polymer composite stock which is hollow at both ends. The resulting rifle is 5.5lbs. Their standard steel Havak uses the exact same design, but made of steel. Accounting for 4” extra barrel over a 16” carbine, that’s about 5lb if the barrel were chopped to the same length (neglecting a little increase for .224” bore vs. .243-.308” bore they use). Comparatively, an AR uses a steel carrier also, which is respectively aluminum in the Havak Element.

Another reason bolt guns are disproportionately heavy is found in the barrel contour. A Sporter barrel will typically start out at 1.2” and then more gently taper toward the muzzle, whereas many lightweight AR barrel contours get skinny immediately in front of the chamber. Easy to add a quarter to half pound of barrel weight just in that difference in contour. We don’t see bolt guns with the equivalent of “pencil” contours, even ones which have small ~0.67” muzzles.

For reference, the Seekins Havak Element, using the exact same design as the standard Havak, but using Aluminum instead of stainless steel for the bolt body and the receiver, everything else is exactly the same. Comparatively, the Steel Havak is $1895, while the aluminum Havak Element is $2,795. So there’s a $900 upcharge to use an aluminum bolt body and aluminum receiver.
 
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Stoner had a vision, of a 6# battle rifle, and used the best and most lightweight parts available, at the time, to achieve that end.
Now, "we" have blurred that goal and made changes here and there, and a 8# AR is considered middling "normal."

Steel has been traditional in bolt arms mostly for being traditional. It gives them a lot of reserve strength for "fill the case" Bubba's out there, too. It's reasonably economic, too.

Steel is a bit more flexible at strength than aluminum, but, a person could well design a bolt gun with an AL receiver. How the market would react to such a thing is the open question.
 
Part of this is market resistance. You could make a bolt gun with a aluminum receiver utilizing a steel bolt head and barrel with a barrel extension similar to an AR. There are a few bolt guns on the market built like that but they tend to be expensive chassis guns. The Barrett ASR/MRAD is an aluminum frame/receiver that utilizes a barrel with barrel extension. The Remington PSR and CSR are of similar configuration though they use a titanium receiver but that could be have been aluminum just as easily, give the integrated barrel extension on PSR/CSR barrels.
 
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Pictured below is my Havak, disassembled. The green circle identifies the parts which remain steel in the aluminum version, the Havak Element. Everything else outside of the circle would be aluminum (less the FPA, of course). The bolt head lugs key into the “breech block,” which simply sets inside the front end of the receiver. You can picture the relative weight loss if that - vast majority - of the receiver were made of a material ~1/3 density of the steel commonly used.


A8E95306-4237-478D-9A23-17A72ABA1E81.jpeg
 
Varminterror said:
Pictured below is my Havak, disassembled. The green circle identifies the parts which remain steel in the aluminum version, the Havak Element. Everything else outside of the circle would be aluminum (less the FPA, of course). The bolt head lugs key into the “breech block,” which simply sets inside the front end of the receiver. You can picture the relative weight loss if that - vast majority - of the receiver were made of a material ~1/3 density of the steel commonly used.


View attachment 910301
Click to expand...
That makes total sense. That rifle also has a mountain barrel contour, which I am assuming would be lighter than a sporter?
 
Varminterror said:
Pictured below is my Havak, disassembled. The green circle identifies the parts which remain steel in the aluminum version, the Havak Element. Everything else outside of the circle would be aluminum (less the FPA, of course). The bolt head lugs key into the “breech block,” which simply sets inside the front end of the receiver. You can picture the relative weight loss if that - vast majority - of the receiver were made of a material ~1/3 density of the steel commonly used.


View attachment 910301
Click to expand...

What holds the barrel and pictured barrel-extension/bolt-lugs into the aluminum receiver? Does the barrel trap that extension in the receiver as it is threaded in?
 
Krones said:
That makes total sense. That rifle also has a mountain barrel contour, which I am assuming would be lighter than a sporter?
Click to expand...

No, heavier. The Havak’s “mountain contour” is deeply fluted, but it’s a larger contour than a light Sporter, so the weight actually ends up a little heavier. The shoulder remains ~0.70-71”, tapering up from there, whereas a standard sporter, not fluted - especially so deeply - might only be .58-.62” at the muzzle. A guy can do that math on what a 0.1” thick, 20” long annular skin of steel weighs versus the ~30% of it they hog out with fluting.

They cut the length on the Element model down short to get the weight down, but they started with a heavier contour than they could have, and ended up with a heavier barrel than they could have. Stiffer? Yes. Sexier? For sure. But not really lighter.
 
mcb said:
What hold the barrel and pictured barrel-extension/bolt-lugs into the aluminum receiver? Does the barrel trap that extension in the receiver as it is threaded in?
Click to expand...

Yes. The bushing slides into the front of the receiver, and is trapped by the barrel threading in place in front of it.

In fairness, it’s not an extension since it doesn’t attach (extend) the barrel, but rather a bearing block or bushing. Case runs into steel bolt head, small steel head lugs run into small steel lugs in the bushing, then large annular surface of the bushing runs into the aluminum receiver. Just translating a big force on a small area into a small force impinging a big area.
 
The A1 AR's were much lighter than AR's of today as a rule. It depends on configuration. My AR15 rifle with a scope and full magazine is heavier than my scoped and loaded bolt action. My M4 carbine is about the same. Then I have another bolt action that is lighter.
 
You CAN make a bolt gun considerably lighter, but they are harder to shoot if you do. There are several bolt gun options from the factory at just over 5 lbs. It isn't hard to build a custom 223 closer to 4 lbs, especially when you start using 16-18" barrels common on AR's
 
All things being equal, a semi-auto will have less felt recoil than a bolt action. So if you lighten the bolt gun too much, not only will strength be affected, but it’s going to be no fun to shoot, either. The AR can be engineered to be proportionally lighter.
 
Well, a bolt gun will start at 6.5 lbs and gain maybe a pound or two after optics, but a 6.5 lb AR can turn into a 10 lb pig pretty quickly.
 
Just one data point, my main prairie dog rifle is a 26" heavy barrel AR-15 chambered in 204 Ruger. It tips the scales at 12-13 pounds empty.

I'd say that barrel profile and length has a major factor in the weight of a rifle whether it is a bolt or AR-15 platform rifle.
 
Steyr Scout rifle uses an aluminum receiver and light contour barrel, along with a synthetic stock to get a 6.6lb .308 bolt action. Not a rifle I want to shoot all day but it is easy to carry.

Steyr put a lot of work into cutting weight. The all steel bolt locks into a barrel extension. Those along with the barrel are the only steel parts. Everything else is aluminum or polymer.

BSW
 
The CZ 527 carbines in 223 come in at 5.9 pounds, per their website, with an 18" barrel. The micro-action does help save weight, but the walnut stock offsets that somewhat. Anyway, that iron-sighted bolt action is almost exactly equal to an iron-sighted A2 style carbine with a lightweight barrel (high 5#s/low 6s).
 
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An interesting twist on this conversation occurred to me this morning:

I have a couple of bolt guns and a couple of gas guns, all purpose built for PRS competition. Getting my bolt guns up to a target 20-25 pounds to stabilize my optics on target while shooting from unstable obstacles and positions is relatively easy. However, despite the common perspective that it’s “so easy for AR’s to get too heavy,” I’ve sort of struggled to get these up over 20 lbs. It’s just too easy to get big diameter bolt gun barrels, whereas you kind of hit a top end limit for what’s available on a shelf for AR barrels. Which of course, is a double whammy (or triple? Or even quadruple?) - the AR is taller and intrinsically less stable on field supports than a bolt gun, (inherently less accurate), (inherently more expensive), and then ends up lighter, such it’s no wonder why gas guns are so much less popular than stick shifters for PRS.

Another consideration just occurred to me in typing the above - there simply aren’t many AR-15 analogy bolt guns available, and comparing AR-15’s to short action bolt guns doesn’t make sense - we SHOULD be talking AR-10’s, which tend to have the expected higher weight ratio relative to a bolt gun. Typically, we’re comparing a short action bolt gun to a mini-action AR-15. A 223rem bolt gun isn’t a 223rem action, it’s a 2.8” compatible, magnum bolt face compatible, 65,000psi tolerant short action which has been made to feed the mini cartridge. Unfortunately, we the true mini bolt guns we do see like the CZ 527 action or the Howa mini are heavy little piggies, partly because their parent actions are also heavy BIGGER piggies relative to say the Rem 700 action - the CZ mini weighs an ounce more than a 700 short action!!! The Savage 25 might be a good example of an “almost mini” action which significantly reduces the overall weight (not difficult to reduce weight from the Savage 10/12 action either though). So it’s also not really fair to compare an F-150 pickup to a Chevy 3500, then say the Chevy is overweight. You’re simply not comparing apples to apples. Equally, comparing a mini action AR-15 which only fits a 2.3” cartridge and struggles to swallow a standard .473” bolt face, let alone a magnum bolt face, and really isn’t designed to tolerate above 55,000psi (enter fudd responses about DTI/Olympic WSSM’s and the defunct DPMS Gen II LFAR’s), against a true short action which swallows 2.8-2.9” cartridges, even with magnum bolt faces, and tolerating magnum pressure standards as well, up around 65,000psi. Inevitably, this makes the bolt gun heavier than it could be if it were designed to the same less burdensome standards as the AR-15. Comparing an AR-10 to a bolt gun brings the weight comparison in line with intuitive expectation.
 
Well, my AR is a pound heavier than my Ranch .300BO. The .300 has a Burris 2-7x. If I take the Aimpoint and light off the AR, they're very close.

MandP15%2001.jpg
 
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