Is my barrel to long?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by fastfire57, Oct 5, 2012.

  1. fastfire57

    fastfire57 Well-Known Member

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    Having a custom 338AI built. I read here that someone did a test starting with a 36" and cut 1" off at a time. Anyting shorter that 34" he lost 150fps per 1" cut off.
    Am I going to have accuracy issues (barrel harmonics)?because of the length 34"?
    Not shure of the taper but the barrel will weigh about 8lbs.

    I have talked to locals that had 34" barrels lighter barrels and had to cut them down to 30" because of barrel harmonics.
     
  2. Joe King

    Joe King Well-Known Member

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  3. Trickymissfit

    Trickymissfit Well-Known Member

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  4. Mikecr

    Mikecr Well-Known Member

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    What 338 are we talkin about?

    You might notice with Dan's charts that velocity nodes appear through the range of both 250/300gr bullets. If he had started beyond 46" he would have seen velocity rise continue with the 250gr -beyond 46". I think with a strain gauge he would have seen shockwave pressure peaks/toughs at cycles down the bore. And this would have been different with another powder.
    His 338/378wm would be ~50gr larger than an improved 338-06.

    Personally, I believe the right barrel length brings a balance between powder burn & tuning quality.
    Too short of a barrel causes ugly bullet release due to high muzzle pressures. This would show up with distance shooting. Too long of a barrel could screw up the chances of reaching good performance, as well as lower probability of first shot accuracy. Trying to counter this with a heavier barrel, means accepting an even heavier gun to produce a gun balance that behaves.

    If I were building a 338 whatever, I'd find(via internet search) a recipe that happened to work for more than one shooter, and not 'tactical' shooters. Look for shooting at ~1/2moa targets at a mid-ranges like 600-800yds, rather than someone walking shots into 5moa steel a mile away..
     
  5. Joe King

    Joe King Well-Known Member

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    I was referring to his findings related to barrel length only. I do not see what case capacity has to with anything beyond what MikeCR stated. Which I completely agree with


    are you saying Dan Lilja never messed with 378 based chamberings? Cause he used a 338-378 for that test
     
  6. Mikecr

    Mikecr Well-Known Member

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    No, I'm sure Dan knew just what he was doing. His test was an exploration, with his conclusion being:
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    For lighter weight, walk-around-type hunting rifles chambered for big cartridges like the 338/378 Weatherby magnum, extra- long barrels are not going to gain any significant velocity increases. As I found out too, long skinny barrels are whippy, especially with the high recoil cartridges and loads. My recommendation is to use no longer than a 30" barrel with a minimum barrel contour of a #4. A better choice would be a fluted #5 or #6 contour. Barrels over 30" are going to have to be heavier to counter the "fly rod-phenonomen" and will probably be too heavy for most walk-around-type rifles. Or rather, too heavy for the gun bearers.
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    30" & 7-8 pound barrel. Sounds rational to me.
    But then, this test did not include accuracy or precision in barrel choice. He implied those factors, which probably represents his experience with the cartridge.
    I'm also referring to a balance, that includes accuracy and field functioning.

    But we don't know for sure yet what fastfire57's 338AI is going to be
     
  7. fastfire57

    fastfire57 Well-Known Member

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    338 Lapua




     
  8. Trickymissfit

    Trickymissfit Well-Known Member

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    when you see the suffix "AI" placed behind a certain cartridge case it means Ackley improved normally. Ackley never did anything with the .378 style case. But he did develope a .338-06 improved round. To the best of my knowledge that's the only .338 he did.

    To further delve into barrel length and what you get is another story. Barrel rigidity becomes a player in this game unless unless we're looking at shotguns. Plus we also get the stress transfered into the bridge of the reciever (becomes the fulcrum point). Lilja once stated in a paper he wrote that a 21" number seven contour barrel was 2.75 times stiffer than the same thing 26" long. I pretty much confirmed this with a C/H Remington barrel (actually ended up about 2.85). This relates a lot to shot to shot consistancey.
    Then there is the issue of barrel harmonics in relationship to bullet travel. But we also want to get the most out of a certain bullet, so everything ends up being a compromise.

    Dan Lilja did some testing with a 34" barrel and said he was quite satisfied with the results. I can't remember the caliber, but it seems to me it was based off the .378 WBY case. Out of curiosity I took a look at three loading manuals to see what they were doing in them. Only one showed the .338/378 loadings, so you must forgive me here. The .338/378 was the fastest in velocity, but used another ten grains of powder to gain 100 feet per second with a 28" barrel. The .338 Lapua used a 24.5" barrel and was down about 200fps, but used about 15 grains less powder to get there. The Remington was down 100fps, but used slightly less powder than the Lapua in a 26" barrel. (I see a trend here already). The .340 WBY mag used even less powder and still got 2900fps with a 26" barrel. I also took a look at the .338 Win. mag for a comparison, and was stunned! They were getting 2650fps-2700fps with ten grains less powder than the .340mag and a 24" barrel. All bullets checked were 250 grain, and I'm sure that when you move upto 300 grain bullets the bigger cases will do much better. What I saw in these charts was a lot of powder being blown out the end of the barrel, and very little gain for anything past 26" in length, and the Lapua with a 24.5" barrel was probably about all that the .338 bore could handle (had it had a 28" barrel, it would probably have been just about as fast as the big case. Even more interesting was that the little .338-06 (unimproved) did 2600fps with about 50 grains of powder and a 23.5" barrel!! The .338AI will do 2750fps with a 24" barrel, and 2800fps with a 26" barrel. I couldn't find my data for the .338RCM, and perhaps somebody can add this to the list.
    gary