What is acceptable velocity variation

Discussion in 'Reloading' started by TheDeicide, Jan 15, 2012.

  1. TheDeicide

    TheDeicide Active Member

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    I am working on making a more consistent load for my rifle, but I can not find the information on what would be considered acceptable, and what would be considered a reasonable expectation. What is possible? I have gotten it to 35 fps variation on some loads, but I don't know if it's possible to get under 10 fps or not.
     
  2. ken snyder

    ken snyder Well-Known Member

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    The longer the range you shoot the more important consistent velocities become. The larger the diameter the bullet the easier it is to achieve consistent velocities. An example would be that with a .375 its pretty hard not to shoot duplicate velocities all day long. with a small cartridge everything becomes more critical. For 6.5 - .30, most should be duplicate. I do not give any consideration to the standard deviation but weight it entirely on the maximum spread from slowest to fastest. About 11 - 14 f.p.s. spread without any odd balls is good enough. I do how ever hit the std deviation button once in a while and it generally comes up 5 to 7 on short string sampling
     

  3. Long Time Long Ranger

    Long Time Long Ranger Well-Known Member

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    I agree with ken. Your maximum velocity spread is what determines how far that weapon is dependable. At 1000 yards your bullet is traveling through the kill zone of an animal for a very short distance as it drops out of the sky. Depending on your cartridge maybe 15 yards through the kill zone. Most people think of the bullet going straight at an animal. It is dropping like a rock at that distance. If your velocity spread varies 30 fps and causes a vertical group of say 8" then you have very little room for error.
     
  4. J E Custom

    J E Custom Well-Known Member

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    Ideally, you should look for single digit numbers. This is not always possible with the smaller
    caliber bullets.

    I try to get all of my 7mm and down to fall within 10 to 15 ft/sec with large bores (30 cal +)
    I try for 9 or less.

    At close range this is not as critical (Under 300 yards) but for long range it is very important.

    This is Just what I try for.

    J E CUSTOM
     
  5. frequent misser

    frequent misser Well-Known Member

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    I like your take on this. That is a good point and one newer shooters don't think about. I killed a coyote one time at 1159 yds with a 308 and he had a hole in the center of his back line. Shows just how vertically a bullet falls at elr. One other point to make is if you don't have a really good chronie don't put to much faith into what your getting for numbers. Take your best load and shoot it on paper at 800-1000 and measure the vertical yourself. I like Broz's method. Shoot a three shot group and let you barrel cool then shoot another three for a six shot group. Tape measures don't lie to you
     
  6. cornchuck

    cornchuck Well-Known Member

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    If a guy has a high variation in velocity, what can be changed to get it under 10 fps?

    Jason
     
  7. ken snyder

    ken snyder Well-Known Member

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    cornchuck, Yes it is part of a normal load development. It is also a product of proper barrel fouling and cleaning intervals.
     
  8. ken snyder

    ken snyder Well-Known Member

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    Guess I should of given a few basic rules to help.

    Never mix brand or lot numbers - cases, primers, powders and sometimes even the same bullets from a different box.

    Brass uniformity and Brass uniformity, they must all be identical twins and without differences such as wall thickness and flash hole - one thing I see people overlook is forgetting to clean the re-sizing lube out of the mouth of the case, some will end up with more or less and that's not good

    Barrels in different states of fouling or cleanliness will not shoot the same velocities ( a forum topic with good but sometimes seemingly conflicting advise)

    It's a willingness to be a robot and perform the same functions the same way every time. It sounds confusing but once you get into it then it is actually as simple as making cupcakes

    The fastest jump start I know of is a book by Glen D. Zediker "Handloading for Competition" ( or similar reading) And all the forum space here on LRH
     
  9. Craig1972

    Craig1972 Member

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    posted duplicate message.
     
    Last edited: Mar 11, 2013
  10. Craig1972

    Craig1972 Member

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    I am not ready to start reloading, but I have been spending the money on quality factory loads and my Variation is much too high. It's at about 60 now. I use Federal Fusion 180 grain for my .300 Win Mag. My highest velocity out of ten shots was 3085 and my lowest was 2964. I believe that gives me a 61fps Velocity Variation. Is that the best I can expect from a Factory load? Even a quality one like Federal Fusion? Thank You.
     
  11. jasent

    jasent Well-Known Member

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    consistency! I sort bullets by bearing surface,uniform primer pockets,weigh every load! Here is a system I use and has helped me improve groups at long range and velocity spread. My 243 shoots es of 3 and sd of 9.
    Hand Loading for Long Range 1: Brass Prep
    Read all his steps.
     
  12. Bart B

    Bart B Well-Known Member

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    In my experience chronographing loads, the cause of large muzzle velocity spreads has nothing to do with the ammo or rilfe. It's how inconsistantly hard the shooter holds the rifle against his shoulder. I've seen a 55 fps difference in average velocity between me and a friend shooting the same rifle and 30 caliber magnum ammo. I could easily cause a 40 fps spread myself holding that 13 pound scoped magnum hard to soft to my shoulder. A friend reported he an another person had over 90 fps average fps difference shooting the same .308 Win. ammo and rifle. Therefore, I'm usually skeptical about quoted fps spreads for a given load.

    If the huge human variable's removed and the ammo's shot in a fixed barrel or a repeatable rest, muzzle velocity spreads will be much smaller. Which is why arsenal and some factory ammo's tested with fixed barrels in universal receivers.

    Ballistic software will show 180-gr. bullets from a .308 Win. will have about 3.7" change in drop for each 10 fps difference in muzzle velocity at 1000 yards. 30 caliber magnums' drop difference for the same velocity change and range is about 2.3 inches. At 600 yards, the drop numbers are 0.9 and 0.6 inch, respectively.

    But often that difference is compensated for by bullets leaving on the muzzle axis upswing of its whip. Slower bullets leave later at a slightly higher angle and strike the same point as their increased drop down range is corrected for.

    If you ammo's shows a 20 to 30 fps spread in velocity, that's good. If it's more, that may not be a problem. Your barrel may well whip such that compensation happens in your favor. Test your ammo at long range and you'll probably be surprised at its performance. I've shot more than a few rounds from prone through a chronograph and at 1000 yards, the vertical shot stringing was less than ballistic software calculated it to be. My barrel whip was compensating for the velocity differences.
     
  13. NMcCullough

    NMcCullough Well-Known Member

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    I could be wrong, but won't ST DEV always be less than ES?
     
  14. jasent

    jasent Well-Known Member

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    yes I got those backwards