This topic contains 24 replies, has 1 voice, and was last updated by  Chris C 2 years, 9 months ago.

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  • #32797
     Chris C 
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    I’ve got a single shot, 1885 Highwall in .38-55. It has a 1:14 twist in a 30″ barrel. I’m shooting a 273 gr bullet that is 1″ long. I’m just beginning to learn about stabilization and haven’t been able to figure out how far downrange it will take my bullet to stabilize. I’ve been shooting at 50 yds, but was recently told it might not even stabilize at 100 yds. Is there a way to calculate what the distance might be?

    Edit:

    If it makes any difference, I’m breech seating the 30:1 alloy bullet.

  • #32811
     rhbrink 
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    I shoot a 310 grain bullet out of a 15 inch twist and it’s very stable at 100 yards you should have no problems. Look up JBM ballistics.

  • #32812
     Chris C 
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    Thanks. Ran my info through the stability chart and the answer came up 4.250, highlighted in green. What does that mean?

  • #32813
     rhbrink 
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    Too stabile! I wouldn’t worry about it shoot and see what happens how fast are you shooting you can always slow it down some as long as you are getting accuracy? I have always wondered how a bullet can be too stabile unless it spins so fast that it comes apart.

  • #32815
     Chris C 
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    I’m shooting at 1450 fps.

  • #32824
     Larry Gibson 
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    A bullet is either stable or it isn’t. Saying a bullet is over stabilized is synonymous with asking how pregnant a pregnant woman is…….

    Those who think bullets can be “over stabilized” are confusing stability of the bullet with the adverse effects of RPM on imbalances in the bullet. Over spinning a bullet can indeed cause inaccuracy depending on the imbalances in the bullet upon launch. It’s why we shoot groups instead of all bullets going through the same hole.

    Your bullet will remain stable down to about 60 fps. There are other external forces that can cause an otherwise stable bullet to destabilize such as nicking a limb, etc. Your bullet at 1450 fps in a 14″ twist has a stability factor of 4.1 +/-. Your bullet is running around 75,000 RPM. Thus if you cast quality bullets and load them properly they should shoot just fine.

    Larry Gibson

  • #32826
     Goodsteel 
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    I gotta watch that one myself. I’ve used the term “over stabilized” to describe a bullet that is experianceing the adverse effects of RPM, just like when I was consoling my wife in her 9th month of pregnancy and came to the conclusion that she was indeed “too dam pregnant”.
    LOL!

  • #32827
     Chris C 
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    Thank you for the affirmation. But it’s my understanding a bullet is not stable precisely when it leaves the barrel. My interest is having some idea how far downrange it probably goes before it stabilizes.

  • #32828
     Waksupi 
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    I think what you are wondering, is when does a bullet go to sleep?

  • #32829
     Rattlesnake Charlie 
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    I think you’re right Waksupi.

  • #32830
     Rattlesnake Charlie 
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    Some info on a bullet going to sleep:

    Post #26 here gives a pretty good lesson on how a bullet goes to sleep:
    https://www.shootersforum.com/ballistics-internal-external/61511-bullet-stabilization-down-range-2.html

    Deep Discussion
    http://benchrest.com/showthread.php?58280-Epicyclic-motion-of-a-bullet-%28video%29

    More Discussion
    http://www.the-long-family.com/bullet_dispersions.htm

    This always provokes some discussion.
    Hopefully it will not degrade into something less civilized.

  • #32832
     popper 
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    Going to sleep refers to a projectile launched badly – for whatever reason. You also have to be concerned about transonic region, To answer your question, change distance to target by a few feet several times. POI kinda forms a circle. Projectile spirals to the target. Tipping at the target can also indicate instability.

  • #32836
     Chris C 
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    Thanks, Charlie…………..now my brain hurts and my eyes are falling out. 😉

  • #32843
     Rattlesnake Charlie 
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    You’re welcome. Now its time for you to go to sleep, huh? LOL

    I view the concept more simply. Ever shot an arrow poorly, and watched it wobble a bit before it gets straightened out?

  • #32849
     Chris C 
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    Can’t say I have Charlie because I’ve never shot an arrow…………….but I get the concept from reading all of the links you provided.

  • #33066
     Sgt. Mike 
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    Rattlesnake Charlie;n13358 wrote: Some info on a bullet going to sleep:

    Hopefully it will not degrade into something less civilized.

    Charlie no I don’t think it will.
    this has been covered many many times

    Chris C. once the bullet is stabilized it is stable like Larry Gibson stated.
    The rotational decay is nominal, thus is not a true sole factor into causing the bullet to destabilize. While a bullet may lose 90% of it velocity is does not lose the same amount of RPM induced by the twist of the barrel
    What will affect your “range” or time of stability:
    1. muzzle velocity the closer you launch the bullet to the speed of sound (transonic region) the sooner in time or range you will see the effect of transonic induced instability
    2. bullet type (cast? Jacketed?) form factor (Flat based? Boat Tail? angle of ogive) Bullet Coefficient as the bullet slows down the bullet will produce differing B.C another note some form factors handle the transonic instability better than others, thus better a more accurate bullet in the transonic region.
    3. Temperature warmer air is less dense than colder air – simple
    4. Altitude higher up again less density (another effect of 3 and 4 is that it changes the seed of sound this is important and then the transonic area is higher or lower) if one is shooting in arctic versus jungle environment the twist rate will be faster for the colder climate.

    looking at one of your questions JBM ballistics produced a SG factor of 4.250 Chris, JBM Ballistics (miller formula) is configured for boat tail bullets which require more twist. But your comment lead me to believe that SG is just a number to you that is confusing so here goes:

    Hence is why some will remark over stabilized ( really spin drift would play in, negatively impacting the accuracy potential)
    Here is a table showing rotational decay of a M80 (USGI 147gr 30 caliber bullet)

    RangeMuzzle1002003004005001000
    Percent of spin remaining 100989693918975
    Bullet RPM198,000194,000190,000184,000180,000176,000148,500

    But here is a important snipet from Berger website:
    quote: The Miller stability formula is most accurate for boat tail bullets, and typically underestimates stability for flat based bullets. In other words, if this stability calculator indicates low stability for your flat based bullet and barrel twist, it’s because the formula is not accurate for flat based bullets. en quote
    so what other formula is used for stability is the green hill formula as a guide (can be used here http://kwk.us/twist.html)
    based on what you have provided 1 ” bullet in a 38-55 (.378″ bullet) at 1450 fps the out put is 1-19.4″ twist
    according to Noe website the closest bullet has a estimate BC of .317

    But what range do you hit transonic range? That is a question of time /distance so I’ll use the calculator at JBM for this the first one I’ll use my altitude (312′) and a 59 degree temperature ( speed of sound is 1115.3 fps) :

    RangeDropDropVelocityEnergyTime
    (yd)(in)(MOA)(ft/s)(ft•lbs)(s)
    0-1.5***1456.21285.30
    501.631366.11131.10.106
    100001284999.30.22
    150-6.9-4.41210.9888.70.34
    200-19.6-9.41147.7798.40.467
    250-39-14.91094.57260.601
    300-65.6-20.91050.1668.30.741
    350-100.1-27.31012.5621.40.887
    400-143.1-34.2980.1582.21.038

    So at 200 yds I’ll be real close to transonic region
    But what about when I shoot in the summer in Arkansas? usually temps are around 90 degrees or hotter my speed of sound will change to 1149.3 fps which is dependent upon altitude and temperature:

    RangeDropDropVelocityEnergyTime
    (yd)(in)(MOA)(ft/s)(ft•lbs)(s)
    0-1.5***1455.81284.60
    501.631371.71140.40.106
    100001295.31016.90.219
    150-6.7-4.31227.4913.10.338
    200-19.2-9.21168.7827.90.463
    250-38.1-14.61119758.90.594
    300-63.9-20.31077.1703.10.731
    350-97.2-26.51041.26570.873
    400-138.5-33.11009.9618.11.019

    Based on these two simple calculations I would state that you should be stable up to 200 yards unless you are in the frozen chosen of the upper US during winter which will slightly decrease the range before hitting the transonic region.

    Now I mentioned spin drift looking at that which can also be calculated via JBM greenhill formula suggest 1-19.4 so I’ll calulate at 1-19″

    RangeSpin DriftSpin Drift
    (yd)(in)(MOA)
    00***
    500.10.1
    1000.30.3
    1500.60.4
    2001.10.5
    2501.70.7
    3002.50.8
    3503.51
    4004.61.1

    Let’s look at a 1-14 twist:

    RangeSpin DriftSpin Drift
    (yd)(in)(MOA)
    00***
    500.10.2
    1000.40.4
    1500.90.6
    2001.70.8
    2502.71
    3003.91.2
    3505.41.5
    4007.21.7

    What we see with the faster 1-14 twist is that I will have to dial in the same correction at 200 yards as I would for the slower twist at 250 yards if the wind is blowing I would add more correction.
    Now is this bad ? no not necessarily the only way to answer is to shoot the rifle at that range. Could the extra rpm increase the diameter of the cone of fire? short answer yes. If I wanted to increase my range of the bullet to shoot stable I would increase the muzzle velocity or shoot in a higher hotter altitude .
    Just remember stability does not guarantee accuracy but without stability you will not have accuracy.
    I hope this short answer helps
    In closing as you are twisting faster than 1-19 I would say you would be stable all the way to 200 yards.
    But honestly I would remeasure your bullet for length though 1 inch sounds short for a 273 gr 38-55 bullet my guess would be about 1.060″ with the gas check on which will change the calculation slightly ( in the Green Hill formula it changes to 1-18″ from a 1-19″ for the longer 0.060″ in length. With the Miller formula the extra length of 0.060″ give 3.572 SG vs the 4.250 SG you got for exactly 1.0″)

  • #33068
     Chris C 
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    Very informative, Sgt. Mike, thanks. I’m going to copy and save all that. Really appreciate you taking the time to give me all that info, even if much of it is confusing. I’ll study it and see if I can get it in my head. My bullet measures exactly 1.00″ and is a flat base, no gas check.

  • #33069
     Rattlesnake Charlie 
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    Chris C, what size groups are you getting at 50 and 100?

  • #33071
     Chris C 
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    50 yds ………only 5 shots

    100 yds………….10 shots

  • #33074
     Sgt. Mike 
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    Chris C;n13691 wrote: Very informative, Sgt. Mike, thanks. I’m going to copy and save all that. Really appreciate you taking the time to give me all that info, even if much of it is confusing. I’ll study it and see if I can get it in my head. My bullet measures exactly 1.00″ and is a flat base, no gas check.

    Chris C I used the Noe version as Al Nelson actually had a blueprint per se on his mold. Hence the 0.060 difference between what we was saying plus I added thickness of the gas check.
    The BLUF is yes you should be stable all the way to 200 yds. Stable means round holes in the target without elongation or hitting sideways. heck with your twist you should be stable even in a Alaskan winter lol best of luck

    P.S. looking at your target at 50 yep yep stable each bullet hole is concentric as well as the 100 yard line

  • #33075
     Chris C 
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    Thanks, Sgt. Mike.

    Yup, you won’t find this bullet in Al’s website. It’s a bullet of my design………hence the “C” designation at the end of the number.

  • #33076
     Sgt. Mike 
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    Chris C the 38-55 is a interesting cartridge indeed

  • #33077
     Chris C 
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    I like it. I’ve this single shot in that caliber as well as a 115 year old Marlin 1893 lever action in it. It’s fun to shoot.

  • #33078
     Rattlesnake Charlie 
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    Looks good. Concentric holes indicate the bullet has no yaw.

    I read somewhere in the past that an indication of a bullet not yet going to sleep is that the group at 50 yds is close to the size at 100 yds. I have not experienced it, so can’t say much.

    And, good groups. You’re getting close to a real winner. I’ve always wanted a .38-55. This ain’t gonna help none.

  • #33079
     Chris C 
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    Aw go ahead, Charlie, it’s makes a good huntin’ round, they tell me. Personally, they only thing I’ve ever hunted or probably ever will get to hunt is paper targets. As far as the 50 yd and 100 yd groups being close to the same………………I’ve not ever experienced it myself either.

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