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I didn't realize barrels moved THIS much!

Discussion in 'Black Rifle Forum' started by nipperwolf, Dec 15, 2012.

  1. nipperwolf

    nipperwolf

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    I knew they moved some, but :shocked:

    [ame="http://www.youtube.com/watch?v=Rte7K_yRTUI"]http://www.youtube.com/watch?v=Rte7K_yRTUI[/ame]
     
    Last edited: Dec 15, 2012
  2. KalashniKEV

    KalashniKEV

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    I'll bet those were hot barrels that were filmed at high speed.

    I'm not too surprised.

    The whole "pencil barrel" or lightweight barrel craze is a fad that will die, IMO.
     


  3. RMTactical

    RMTactical www.AR15pro.net CLM

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    That was a lot of movement, more than I expected to see in the slow mo as well.
     
  4. cowboy1964

    cowboy1964

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    It's not the thickness of the barrel so much as the fact that's it's free floating vs non?
     
    Last edited: Dec 15, 2012
  5. M&P15T

    M&P15T Beard One

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    I have a free-floated barrel, and that movement is about what I would expect to see. But then I had seen a previous video that alerted me to how much AR15 barrels move, so it's no surprise.

    And we're also seeing another reason my FA/rapid fire is inaccurate. Shoot fast enough and the barrel hasn't stopped moving when the next round heads out.
     
    Last edited: Dec 15, 2012
  6. mjkeat

    mjkeat

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    I wouldn't say the lightweight/pencil barrel thing is a fad. 1968 (?) to 2012, not fad status.
     
  7. Looks like the barrel starts flexing right after the bullet has left the barrel. At 0:43 in the video, you can see the bullet which is already about 2 meter away from the muzzle and the barrel starts flexing at the same time when the bullet is long gone. The reason for the barrel flex delay is the inertia of the barrel. I'll bet if he replaces that compensator with just an symmetric flash hider, the barrel flexing would reduce itself by a lot, free floated and non free floated.

    The gas pressure between the breech face and the bullet which then escapes through the upper compensator slits right when the bullet is about to leave the muzzle is trying to push down the barrel hard in just a few thousands of a second. All the down pressure/energy starts building up in the barrel till it's starts flexing downward first and then up. But the bullet is already a few meter away from it all. Due to the inertia delay.

    I believe barrel flexing has more to do with the muzzle device than with free floated or non free floated designs. Either way, I think barrel flex has little impact on accuracy, well at least in semi auto rifles because the flex starts after the bullet has left the barrel. It might have an impact in full auto rifles since the flex might not stop till next shot gets fired. But who cares, full auto fire doesn't give you much accuracy anyway.
     
    Last edited: Dec 15, 2012
  8. Ruggles

    Ruggles

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    That is some wiggle alright, more than I would have thought as well.
     
  9. mac66

    mac66 Huge Member Millennium Member

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    Which brings up the question, shouldn't a non floating barrel be more accurate in sustained fire? It would be more rigid wouldn't it?
     
  10. KalashniKEV

    KalashniKEV

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    Everything old is new again. The "pencil barrel" craze started in 2010 with DD leading the charge, and just as operator feedback drove the evolution from the A1 to the M4, it will again teach us the same lessons and lead us down the same path.

    Shaving that weight off the barrel has an adverse effect on performance.

    If there was no correlation between rigidity and barrel weight, then there would be no reason to run anything but a pencil barrel.
     
  11. WoodenPlank

    WoodenPlank Who?

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    Nope. It's not really stiffer, and you still have outside forces acting on the barrel, which hurts repeatability.
     
  12. RWBlue

    RWBlue Mr. CISSP, CISA CLM

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    It is the question of how much do you carry a gun vs. shoot it.

    If I were SF and expected to only have a gun when I needed to shoot it....HB and long.

    If I have to carry it for long periods of time and NEVER expect to need to shoot it, then pencil and fairly short.

    The problem comes, what do you do when you are outfitting a military. Some of the people are SF, but most are support people. Of course everyone wants to be armed like the cool SF guys until they have to carry all the crap all the time.
     
  13. mjkeat

    mjkeat

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    I'm hoping so. I turn 35 in a few days. The years are starting to show.

    I think LWs are a good general purpose option. It can remain slung the better part of a day w/ minimal sacrifice to comfort yet make the shot when needed.

    For a general purpose carbine I see no reason for anything other than a LW barrel.

    If I want to shoot for groups I pull out the SS 410. I wouldn't want to have it slung all day considering other options.

    So, though technically you're correct does it really make a difference? What are the numbers? Are we talking a 4moa difference, or more? Less?



    Sent from my DROID RAZR using Tapatalk 2
     
  14. KalashniKEV

    KalashniKEV

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    I see no reason for a pencil or LW barrel unless you're measuring every ounce that goes in to the rifle. The barrel is just not an area that interests me in shaving ounces and cutting weight at the expense of performance.

    Look at the rail/forend/HGs first- maybe get a modular.
    Look at your forend accessories- maybe go to a pistol light, handstop index over FG, etc.
    Look at your optic and furniture- if you're running an Elcan and a UBR... :faint:

    Even if I'm doing fielding for a carry more/ shoot less organization, that's still not a sacrifice I'd be willing to make without good reason- like hiking or climbing.

    That would be after I sourced the lightest available rail, T1, K Grip, and N type stocks.
     
  15. RMTactical

    RMTactical www.AR15pro.net CLM

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    I tend to agree. Unless it is a machine gun or a sniper, what is the point of a HBAR anyways? I like the lighter profiles.
     
  16. mjkeat

    mjkeat

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    I have that all to complement my LW barrel.

    My question remains. I asked, "So, though technically you're correct does it really make a difference? What are the numbers? Are we talking a 4moa difference, or more? Less?" What's the sacrafice?
     
  17. RWBlue

    RWBlue Mr. CISSP, CISA CLM

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    I own an HBAR and frankin gun with LW barrel. It does make a difference to me.

    I also want you to think about all the hunters out there and the rifles they carry over hill and dale.
     
  18. crazymoose

    crazymoose Nonentity

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    The problem with watching the evolution of barrel shapes used in the military is that you have to remember that they suffered under the requirement of being able to mount the M203. I like a medium weight barrel as well, but the military did it backwards, in my opinion- instead of a barrel tapering from chamber to muzzle, they have a light barrel under the handguards and heavier toward the muzzle. It's not as rigid and it's more nose-heavy, compared to a barrel of the same mass in the tapered profile.

    That said, I prefer a medium weight barrel more for its ability to handle heat and maintain accuracy better as it heats up. If you're talking about accuracy before the barrel heats up, there are minimal differences between a pencil barrel and HBAR of otherwise identical machining/quality.

    Another thing to keep in mind when watching the video: the barrel stops flexing before the bolt even returns to battery. Even in FA fire, it's not as if the barrel is flying around like a cartoon fire hose as bullets are leaving the muzzle.
     
    Last edited: Dec 17, 2012
  19. 56belair

    56belair

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  20. RWBlue

    RWBlue Mr. CISSP, CISA CLM

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    +1, bad design.