How much jump do you use?

Discussion in 'Reloading' started by stonehands1, Mar 24, 2015.

  1. stonehands1

    stonehands1 Well-Known Member

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    I seems every rifle likes a different amount of jump. And for any given rifle it seems that for every different bullet you use you can't use the same amount. Some like it tight some loose. My question is has anyone put together a list of which bullets like it tight and which ones like it loose? Maybe it has something to do with the weight or shape of bullet.
     
  2. gohring3006

    gohring3006 Well-Known Member

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    As a basic observation, I have found Tangent ogives are very forgiving and like some jump. Secant is less forgiving and like to be close to the lands. (with the exception of Hornady Amax, which is a secant according to Hornady.I can get these to shoot where ever I seat them, which leads me to believe they are a hybrid design.) That leads to a hybrid which is the best of both worlds.
     
  3. Mikecr

    Mikecr Well-Known Member

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  4. Rick Richard

    Rick Richard Well-Known Member

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    Close to what is recommended by Berger. I find VLDs come in somewhere from .010 to .030 and Hybrids somewhere between .040 and .060 for most of my guns.
     
  5. Corey Schwanz

    Corey Schwanz Well-Known Member

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    As said above, tangent ogive bullets tend to be more forgiving and will tolerate more jump. Secant ogive bullets can be very sensitive and usually require a bit more load development work to find the sweet spot. In our case, closer to the lands is traditionally better than way off (at say SAAMI lengths) but every gun is different. What works well in one rifle may not in another.
     
  6. stonehands1

    stonehands1 Well-Known Member

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    Great. Thank you for all the informative responses.
    Next question:
    Let's say I have picked a Secant, high bc bullet and I want to use it in a couple different rifles. One is a high power magnum that has lots of cup pressure and slow burning powder like a 300rum. The other is say a .308.
    Could I assume that I will have to set the bullet tight to the lands in both because the bullet is the same. Or does the powder burn rate, and for lack of a better word, size of the explosion pushing the bullet have much to do with it?
    Thanks
     
  7. stonehands1

    stonehands1 Well-Known Member

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  8. brentc

    brentc Well-Known Member

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    I don't think it's all that random. For hybrids, .050 off is a sweet spot in several of my rifles. For VLDs, they either shoot well close to the lands .010 - .020 or at .070 off.
     
  9. Mikecr

    Mikecr Well-Known Member

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    I haven't seen an actual pattern with ANY bullets.
    The only pattern I'm aware of in seating is with tiny underbores(6PPC, 30br, etc) loaded to reach extreme pressure nodes. These will need bullets into the lands(ITL) regardless of type, to get high starting pressures.

    Anyway, because seating is the single biggest adjustment to results(way bigger than powder), I go ahead and run a full blown version of Berger's seating test right up front. This, during brass fireforming.

    With best seating determined(coarse), and all cases at stable capacity, I'm ready for powder testing. With best seating AND best powder load, I tweak seating within a 10thou window of prior tested best, to shape grouping.
    Then I move into cold bore load development, but seating with that bullet/barrel will never need to be adjusted again.

    Change the bullet or chamber and it's start over for seating.
     
  10. SabreCross

    SabreCross Well-Known Member

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  11. Bigcat_hunter

    Bigcat_hunter Well-Known Member

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    Yep. With my last two rifles I was convinced they would not should VLD type boat tail secant bullets until I tried the Berger seating depth trial. Both shoot bug holes at .130 of the lands.
     
  12. Clark

    Clark Well-Known Member

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    On bolt and single shot 223 and 6mmBR, I jam into the lands, not so much so I can't pull it out.
    Rodent hunting is like going to the range.

    On 270 and 7mmRM, I seat at 3.34" no matter how far from the lands.
    Ruminant hunting is like going to war.
     
  13. brentc

    brentc Well-Known Member

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    Maybe my results are coincidence, but I've got enough of a sample size to see that if I run a ladder test with berger hybrids at .050 off the lands, I'm within a few rounds of finding a load that produces .2s and .3s. Of course, my only objective is to produce precision hunting ammo, not benchrest.
     
  14. FearNoWind

    FearNoWind Well-Known Member

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    I have specific load data for each of my rifles and for each load. But the data I have is unique to my rifles and, unless by some stroke of luck things just happen to fall into place, my data will not work for your rifle. Point - when you work up a load keep good notes. When you make changes make them one at a time.
    Respect the uniqueness of your rifle. It deserves nothing less.