Great 20 Caliber Guide!

Discussion in 'Small Stuff--22s, 20s, and 17s' started by dimecovers3, Aug 26, 2005.

  1. dimecovers3

    dimecovers3

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    Thanks for all the info on 20's. I spoke with Dakota yesterday and the brass will be here soon and loaded ammo,Black Hills)will be here for Christmas. I wonder from reading the guide that if 40 grains are iffy with 1/12 why can't a 11 1/2 shoot the 32's and the 40's. This would seem to be a solvable problem.

    Steve
     
  2. kory

    kory

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    Steve,

    Which ammo is Black Hills making? Tac-20 or 20 VarTarg?

    Kory
     
  3. smike308

    smike308

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    Kory--
    Great job on the 20 cal page. A lot of worthwhile info there. I have a question about the ballistic chart at the end of the page. It shows that the Hornady 40gr,B.C..275) seems to outperform the Sierra 39 gr,B.C..287)in both drop and wind drift. I would have guessed it to be the other way around given the higher BC of the Sierra.
    TIA--
    Mike
     
  4. dimecovers3

    dimecovers3

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    I was told the ammo will be loaded from the Laupa brass after it gets here with three different bullets,don't know which three). The guy on the phone said it was the Tac 20, but that may be because I asked about the Tac only. I never asked about the Vartarg, but the brass is due here also for it. You would have to check with Dakota to find out. I would take all this with a grain of salt. They have pushed back the dates on this twice already.

    Steve
     
  5. kory

    kory

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    Mike,

    Thank you for the complement. I noticed that also. There are two reasons for that. Firstly, it has to do with the 1 grain less weight. The Seirra is 2.6% lighter than the HDY, so that explains the drift, but not the drop. However, the data is slightly misleading in that Seirra used different ballistics coefficients at different speeds, while for HDY, the same BC was used at all speeds.

    Ballistic Coefficients to Velocity Bounds for Sierra 39 gr BK
    1. 0.287 at 3600 fps. and above.
    2. 0.270 from 3400 to 3600 fps.
    3. 0.255 from 2800 to 3400 fps.
    4. 0.236 from 1900 to 2800 fps.
    5. 0.180 at 1900 fps. and below.

    So I would imagine the Sierra data is closer to real life than the others. I was not able to find the BC for different Velocity Bounds for the other bullets, and the Seirra Software came pre-programmed with the info for the their own bullets. In a snse, that gives their competitors a false edge.

    Regards,
    Kory
     
  6. smike308

    smike308

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    Kory--
    Thanks for the quick response. What you said makes sense of it. When I first looked at the data, I did a lot of head scratchin' trying to figure it out. Never thought of that.
    Thanks & Keep up the good work--
    Mike
     
  7. Forum Boss

    Forum Boss Administrator

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    Mike,

    We are recalculating the Sierra Data using a "manual over-ride" to assign specific BCs to particular velocity ranges. The Sierra ballistics program Kory used has an "automatic" calculation for all Sierra bullets. It appears the Sierra program employs a blended or averaged BC that underestimates the effect of the superior BC at the higher velocity values.

    Initial runs with a manually-inputted .287 BC value for the 39gr BK at the higher,3600+ fps) velocities do show less drift & drop for the Sierra 39 than the Hornady 40 at the longer distances. So your suspicions were correct!

    Just goes to show that you can't necessarily rely on software 100%.

    And thank you for bringing this to our attention. We suspect this may also lead to some changes in the Sierra software itself.
     
  8. Asa_Yam

    Asa_Yam

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    Nice article, but....you are making an apples to oranges comparison when benchmarking almost any of the .20 caliber rounds to a .223 Remington!

    - Based on bore diameter alone, a .224" diameter projectile needs to be 1.32x the mass of the .204" diameter projectile you are comparing it to. Thus, scaling up a 32 grain .204" projectile to .224" results in a 42 grain projectile. A scaled-up 40 grain projectile would weigh about 52 grains.

    - A direct comparaison would also scale up the powder charge relative to bore diameter. This gives you velocity, along with a suitably scaled projectile.

    - Barrel wear is related to many things, but a big one is the amount of powder being poured through a given bore diameter. Smaller bores may have an advantage here, as there is relatively more mass to soak up the heat. However, I wouldn't expect the difference to be more than 10% in favor of the .20 caliber barrel.

    There are some issues with scaling factors, but the points above give you a better means by which to find a larger caliber analog to any smaller caliber round.

    Based on the information above, a direct comparison of cartridges would result in the following:
    - .20 BR = .220 Swift
    - Tactical .20/.204 Ruger/.20 PPC = .22-250
    - .20 VarTarg = .223 Remington

    Granted, while performance will be equivalent, you will always get less recoil with the smaller rounds. This is a good thing, as it means:
    -Less movement of the firearm,lower recoil and muzzle climb), AND;
    -Faster follow-up shots.

    Asa
     
  9. Forum Boss

    Forum Boss Administrator

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    Asa,

    You've made a lot of good points and your approach is sound. The reason there are a lot of cross-references to the .223 Rem is because it is the still most popular centerfire round and is the most-used centerfire varmint round by far.

    What we hear from smiths and gunshop owners is that when people are considering a 20, the first question is "what will it do that my .223 won't do better?" The next question is "OK, if I go with a 20, what are my options?" That is why we went to the effort of comparing the Twenties to a .223 Rem, and why we covered a range of popular cartridges, not just the .204 Ruger or 20BR.

    The bottom line is that if any small cartridge wants to succeed with shooters it has to offer some performance edge not provided by a .223 Rem. In the case of the Big Twenties you get higher V and flatter trajectories with the .204 Ruger, Tac 20, and 20 BR. With the 20PPC you can, employing benchrest reloading methods, get a definite accuracy edge over the .223 Rem. With the VarTarg, you get reduced bolt thrust and increased efficiency in a very small form factor that allows the round to be shot in super-compact actions. Personally, I'd love to build up a 20 VarTarg Ackley on a Hall Falling Block action with a full carbon stock. It would be a wonderful "walk-around" varminter.

    [​IMG][​IMG]
     
  10. CajunBlake

    CajunBlake Silver $$ Contributor

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    Kory - very well written and educational 20 cal. page. I'll be sure to keep in touch and share with all my load data and opinions once my 20PPC short is completed.

    Editor - I too have longed many years for a Hall "F" action. I beleive Alan,Hall) no longer offers this action. I shot one at a BR match several years ago and I still dream about owning one. My biggest problem would be deciding upon which caliber.

    CB <*)))>{
     
  11. Wild_Bill

    Wild_Bill

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    Hi Kory i think your article was verry good i went looking and missed 1 thing a 20K Hornet i would have loved to see one as i think it could be the best calibre for an improved hornet i just thought it might have been there. I do understand that it is verry hard to compare every thing though from my own experiences well done would love it if in the future you had any info on the 20 K Hornet to add it would make the article even better.

    Cheers good shooting Bill
    Australia
     

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