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Thread: Fuzzy Ballistics

  1. #1

    Fuzzy Ballistics

    Hey Good mornin fellas.

    I got some fuzzy thinking going on, and I'm hoping one of you can sort me out. Here is what I got:

    Modern long range guys I have heard said that things go wonky out at extreme ranges. I think I heard some .338 Lapua guys saying that when their bullets go subsonic out at some ridiculous range like 1300 or 1400 yards or so - everything goes off the rails and hits beyond that become a matter of luck as much as marksmanship. As the modern centrefire cartridges get smaller, those ranges get shorter. (I think the .308 guys said they go subsonic at 800)…

    Whatever!

    But after hanging out here and with some help from you guys - I am doing alright with my 45-70 going approx. 1180 FPS. It does well out to 300 which is the maximum extent my range goes. But... my loads are starting off at almost subsonic velocities, and I don't think even my fine home made Postells come close to the BC of say, a match .338 pill.

    I guess my question is... why do our guns shoot so well at subsonic velocities and the modern jacketed calibres don't? Is it entirely a matter of bullet mass?

    Hope ya got something fun lined up for the weekend - your two cents, as always, is sincerely appreciated!

  2. #2
    Boolit Master pietro's Avatar
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    .

    It's a function of bullet shape & stability at various speeds.

    .
    Experience is a wonderful thing - It lets you recognize a mistake, when you make it again.

  3. #3
    Boolit Master
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    Its well known with range shooting ....a few FPS more vel in a 308 load,and accuracy improves greatly in 1000m shooting.The reason is that the trans sonic zone of velocities from approx 1400 fps ,down to around 1100 fps involves problems with drag transition where shock waves collapse and reform randomly around the bullet,destabilizing it.Once below 1100fps ,there is no shockwave ,as the bullet velocity is subsonic,and streamline flow of air over the bullet in a predictable manner......If you re over 60 ,you will be familiar with the old movies where the experimental jet plane always starts to vibrate and breaks to pieces as the hero testpilot breaks the soundbarrier.

  4. #4
    Boolit Grand Master

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    It isnt the subsonic or the supersonic velocities that are a problem its the transition in flight between the 2 that is. Your 45-70 isnt showing it because its staring out sub sonic and staying there all the way to the target. When a bullet foes from supersonic to sub sonic the transition disturbs the flight of the bullet. This also appeared in the early jet plane test flights, sometimes violent enough to cause loss of control and crashes.

    I have shot the M1A out to 1000 yds in 308 and it can be done. I used the 173 grn special ball bullet later the 175 grn sierra when it became available. With a good load it would just stay above and gave some very good scores. Some of the new vld designs do much better yet. My match rifle was a 243 with 1-7 twist hart barrel. At 1000 I shot 105 JLKs these were a vld design and a BC of just over .6. BC s a combination of weight and form. Also velocities play a part in it also.

    I have figured the BC for the 550 grn old west silhouette bullet I shoot at 1150-1200 fps at .460 (if memory serves). Sub sonic dont drop velocity like the super do. This bullet starts out 1150 -1200 fps and is still in the 1050-1080 range at 200 yds out. The 223 Ive done start out around 2900 fps and are down to around 2450 at 200 yds.

  5. #5
    Boolit Master
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    These two fellas gave you the perfect answer, you could not ask for anything more. Love this site.

  6. #6
    Boolit Grand Master


    Larry Gibson's Avatar
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    Other than the above some bullets will make the trans-sonic transition w/o losing a lot of accuracy, becoming dynamically stable or losing stability entirely. Generally a flat based, round nosed bullet with high sectional density makes the transition smoother most often without a loss of stability if properly stabilized to begin with. The reason being, in the flat based round nosed bullet, the center of form, the center of gravity and the center of pressure are closer together.
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

  7. #7
    Boolit Grand Master

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    Larry not to hi jack the thread but for awhile in my long range / coarse rifle at 600 yds I shot a Starke 6 mm vld flat based 105 grn ( while it was available wish Id stocked a bigger supply). At 600 it gave better scores and wind bucking than the Boat tail version did. I never tried it at 1000. I believe this may have been partly to the slightly shorter length on the bullet. 115 grn bergers also performed well.
    Long range the transition can be hard to predict how it will perform. Ive seen loads that performed well at 600 go to pot at 8 9 1000. Ive also seen loads that shot at 200 that were no good at 600. The only way to know for sure and certain is to shoot them full distance.

  8. #8
    Boolit Grand Master


    Larry Gibson's Avatar
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    Another thing about "how good" some bullets make the trans-sonic transition back down to subsonic is how close the make that transition to the target. The closer to the target the transition occurs the less noticeable the adverse affect will be. Or; the greater the distance between the transition and the target the greater the adverse affect will be.
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

  9. #9
    Boolit Master marlinman93's Avatar
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    All my loads are above 1126 fps for my long range guns. All are old BP cartridges, but shot with smokeless and most around 1300-1400 fps with cast lead. I shoot them out to 1,000 yds. and I'm certain they go drop below 1126 fps before striking the target. Most are .45 or .40, but i also shoot my .38-55 out to 650 yds. on occasion.
    I don't see things going totally bonkers, or hitting shotgun patterns just from dropping below sonic levels. I've read the same things about it, and I believe it's true. But it's really a question of how much it affects the bullet, and whether the effect is the same shot to shot. I can't answer that, except to say I'm not seeing something to indicate it's making huge changes in accuracy.

  10. #10
    Boolit Grand Master

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    The biggest thing is to keep a good "book" so patterns and results are shown over several days. The longer these are kept the better the data becomes. For long range knowing the zeros for a given range, at long range a small miscalculation in setting can result in a miss. The newer more efficient rounds and better bullets VLD bullets with much higher BCs make the long range much easier. It is a benefit to chronograph the loads figure the actual bc at that velocity and then make a chart for these numbers. Its much more accurate.
    I always took the lap top to sate long range matches. New shooters with out a zero I could run the numbers ad give them the come up from 200 yd zero. If they gave me good velocity BC numbers They were inside 10 ring for elevation ( I couldnt read wind for them on the line LOL). New shooters were normally squaded with an experienced shooter to keep the wind under control. Most went home with a very good experience behind them. Long range requires more attention to detail and also a good spotter scorer coach when allowed.

  11. #11
    Boolit Master


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    Another "strange one" is .22LR target ammunition. It's MV is below the transonic velocity for a reason. Good posts above.
    Don Verna

    NRA Endowment Member

  12. #12
    Boolit Master
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    Modern bullets are a different sort of thing. The nose designs don't work as well as a typical black powder long range bullet once velocity drops, also the boat tails that many of them have reduce the base drag so they become unstable more easily. These days most long range black powder competitors start their bullets above 1300 fps with no instability problems. I don't ever worry about that problem at all, with the exception of my .32-40's. The bullets and twist rates I am using generally show a little tipping at 200m with black powder so I haven't ever tried shooting them further.

    Chris.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check