Barrel Flex?

[Simon_Belmont]

I just received my DD 14.5 LW Middy upper with a 12 inch LITE rail. While fingering my toy I noticed that I can bend the barrel slightly by squeezing the barrel and rail together. I really doesn't take that much force to visibly see the barrel flexing torward the rail. Is this right? I like the weight savings on the liteweight barrel contour but It looks like my barrel will break if it is hit off of a wall or something. Anyone care to shed any light on this?

Thanks

[mhanna91]

I would like to know about this too. That was one of the first things I noticed after I put my Troy 13.8" MRF on my BCM 16" gov. profile midlength.

[dennisuello]

don't squeeze then. both rail and barrel will bend toward each other, they are not made from unobtanium, that's completely unbendable. you have quite a bit of leverage that far away from where the barrel and rail both mount to the receiver.

[Joeywhat]

It won't break.

[Simon_Belmont]

So your barrel is flexing slightly with a govt profile? That make me feel alittle better. I tried messing around with a bone stock BCM govt profile barreled m4 upper but the results were inconclusive.

[Simon_Belmont]

So its safe to say that ANY profile barrel will bend slightly when pinched with a ff rail extending out to muzzle?

[bigdog2003_99]

my noveske 10.5 flexes alot, it looked like my m4-2k was backing itself off or very loose. it scared the poop out of me while my buddy was shooting, as long as i dont get a baffle strike its no big deal though

[mhanna91]

Well I figured that the barrel steel has to have some elasticity in it or else it would snap off the first time it hits pavement. We also have alot of leverage with the longer rails. It just seemed odd to me that it was able to bend that much.

[Simon_Belmont]

Well I figured that the barrel steel has to have some elasticity in it or else it would snap off the first time it hits pavement. We also have alot of leverage with the longer rails. It just seemed odd to me that it was able to bend that much.

So do all barrels bend like that when bench supported out by the muzzle regardless of whether it is FF or regular plastic HG's?

[jasonhgross]

I noticed the same thing on my BCM govt profile mid-length. I actually noticed less flex with my DD 14.5 LT weight mid-length.

[Suwannee Tim]

Young's Modulus (http://en.wikipedia.org/wiki/Young%27s_modulus)

The Young's modulus is the ratio of stress (pounds / square inch) divided by strain (inches deformation / inch). When you apply a force to your barrel, that is stress. When the barrel moves in response to the force that is strain. This ratio defines how stiff a material is. Stiffer materials move less under the same stress. An aluminum object will move three times as much as a steel object of the same size under the same load. The modulus of iron is roughly 30*10^6, thirty million as is that of cobalt, manganese, nickel. Chromium is somewhat higher, about 45*10^6 as is vanadium. All iron alloys, tool steel, structural, stainless, inconel, all of them have approximately the same modulus, 30*10^6. This means how stiff the barrel is is independent of the alloy it is made of. The other factor that defines the stiffness of an object is it's dimensions. Generally, stiffness of a given shape is proportional to it's width, the cube of the thickness and inversely proportional to the cube of the length. For example, a 2X8 is twice as stiff as a 2X4 bent the easy way but eight time as stiff bent the hard way. A 2X4 8 feet long will bend eight times a much under the same load as a 2X4 4 feet long. An object twice as wide is twice as stiff, an object twice as thick is eight times as stiff and an object half as long is eight times stiffer. If you double the diameter of an object it is sixteen times as stiff because it has twice the width and twice the thickness.

Toughness is a different thing, it is the opposite of brittleness and is a measure of the amount of energy it take to fracture a material. This varies widely with alloy and temperature. A material may be very tough but not very strong, very strong and not very tough, tough at room temperature but brittle in the cold. The engineer specifies all materials so they are adequately tough under anticipated conditions. The Liberty Ships of WWII were made of steel that became brittle in the cold of the North Sea. They broke in half and sunk. Steels must be designed to have adequate toughness under the coldest conditions they will face or they will break, just snap.

Strength is yet another thing, it is the measure of how much stress (pounds / square inch) it takes to deform a material to the point it will not return to it's previous shape. Deformation may be elastic or plastic. An object (such as your gun barrel) deforms elastically then returns to it's previous shape. Other objects, say a beer can you crush has been deformed plastically. Stregnth varies widely with temperature and alloy. Generally when we talk about "hard" or "soft" we are talking about strength. Most structural components and all firearms components are designed so they never (hopefully) deform plastically.

[kartoffel]

So do all barrels bend like that when bench supported out by the muzzle regardless of whether it is FF or regular plastic HG's?

Yes. Regular handguards attach to the barrel and they move with it, so you just don't notice it as much.

[ucrt]

.

Just curious, how do you know the barrel is flexing and not the hand guard?
I'd think the hand guard would at least be doing some, if not all of the flexing?

.

[5pins]

If you want to see barrel flex take a look at this video and about 1:39.

http://www.youtube.com/watch?v=5hKaPkvOtEo&feature=player_embedded

[BufordTJustice]

If you want to see barrel flex take a look at this video and about 1:39.

http://www.youtube.com/watch?v=5hKaPkvOtEo&feature=player_embedded

Holy Shit. I had no idea the barrel whipped-around like that. Hopefully Ned or Bill will weigh-in on this.

Great video, btw. :)

[Weaver]

Yes, of course barrels flex when lateral pressure is applied. That's why people went to free-float rails in the first place - hell, I used to be able to flex an M16 barrel using a medium-tight shooting sling enough to pull my rounds a good 3-4 inches at 25m.

No, your barrel won't break. Take it out and shoot it.

[ucrt]

If you want to see barrel flex take a look at this video and about 1:39.

http://www.youtube.com/watch?v=5hKaPkvOtEo&feature=player_embedded

=====================================

Man!! that's some whip there! Hard to tell but that barrel looks kind of thin...maybe a DD pencil profile?

Just wondering, has anyone seen an upper crack or break? The aluminum upper seems like it would be the weakest link and that eventually it would fatique with a barrel whipping like that or a rifle getting dropped??

.

[SA80Dan]

.

Just curious, how do you know the barrel is flexing and not the hand guard?
I'd think the hand guard would at least be doing some, if not all of the flexing?

.

Yep, I'm of the same opinion. The rail will be going towards the barrel, and vise versa.

[justin_247]

If you want to see barrel flex take a look at this video and about 1:39.

http://www.youtube.com/watch?v=5hKaPkvOtEo&feature=player_embedded

Beat me to it! I was going to post exactly the same video.

He's using a DD lightweight carbine barrel.

[JSantoro]

Gents, all barrels whip to some degree or other. It makes more of a difference with the USGI M4/M16 variants in which the railed forearm is tied in with the barrel. Enough extra ancillary equipment (bipods, lasers, lights, kangaroos, mariachi bands, etc.) have a chance of changing the jump-angle of the barrel and thereby the flight of the round.

With free-float systems, the barrel itself remains largely unaffected. If you watch some of the more high-res, high-speed videos, you'll note that the bullet, barring some cataclysmic occurrence, is out the muzzle prior to the barrel-whip beginning. It's also happening so fast that it stops while you're thinking about pressing a follow-up shot.

Where you'll see an impact on POI is when you have an optic that straddles the receiver and a free-float forearm, or where you have a forearm-mounted iron sight. If something is flexing the forearm, you will likely see a POI shift of some sort....hence the reason for canteliever mounts for RDSs and things like the LaRue SPR series mounts for magnified optics. Keeps the optic out of the forearm-flex equation. How great a POI shift depends on a great many factors, starting with whether you really care or not.

No monolithic or same-plane rail automatically equates to the optic being totally isolated and still being perfectly in tune with the barrel, but then, those worried about that sort of thing are generally worried about usage other than that of the usual carbine employment and take appropriate steps.

[MistWolf]

Barrels are made to be tough, not brittle. The barrel will bend with enough force, but it won't break