When the bullet goes transonic/subsonic

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by sako-75, Aug 23, 2007.

  1. sako-75

    sako-75 New Member

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    Hello everyone

    I have read much about supersonic range, and that when a bullet goes into the transonic-zone, and in the end going subsonic, it looses much of its stability and the BC drops to a much lower number. But what does excactly happend to the bullet, I mean, other than being more affected by wind? Will the accuracy decrease, even if there was no wind to affect the bullet? And is it possible to calculate and predict the path of the bullet during the transonic area, using some kind of formulas or a ballistic computer?

    I have read somewhere that some 50 caliber bullets, like the 750 grains AMAX (with a BC of 1.050), are very stabilized compared to other bullets when going transonic. Is this true? I have also heard the same thing about the M33 Ball, but the M33 Ball does only have a BC of 0.670. But I think that Carlos Hathcock (the legendary USMC sniper) had a confirmed kill at 2500 yards, using a 50 cal M2 machinegun firing M33 Ball ammunition (or pherhaps it was M2 ball, but these two bullets have the same BC), and at 2500 yards, the M33/M2 ball would have been in the transonic zone for a long time? How did he manage this shot in that case?

    Sako75
     
  2. Michael Eichele

    Michael Eichele Well-Known Member

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    This is an incrediably complicated subject. I myself do not have all the answers in this regard or 1/2 the answers for that matter. I dont know anybody that does. What I do know is that most standard projectiles will loose enough of their stability at the transonic wall to cause them to wobble. The wobble gets increasingly worse and then they begin to "tumble". First they will "key hole" into your target. This means they hit nose first but at an angle. When they tumble they ussually hit the target sideways. If an airplane didnt have wings and other stabilizing factors, they would do the same thing.

    Some bullets will react different than others. Depending on balance, the stability factor of it due to the twist rate used and other factors some may be able to withstand the forces of the transonic wall and even though they are affected by it will regain their stability after reaching subsonic velocities. A short for heavy weight ratio bullet spun very fast will typically make it through the wall and keep going. Some bullets also increase in BC after going subsonic. Why does this happen. I honestly dont have the answers to those questions. I just know some will do different things with different twist rates. Overspinning a bullet though leads to other issues also so I personally wouldnt recomend getting a new barrel with an ultra tight twist either.

    As far as Hathcock's 2500 yard 50 cal. kill, it is hard to know just what the real BC of the bullet was and we can assume it was close to published but do we know the drag model of it? Depending on the drag model it could have been super sonic past 2500 yards in the enviornment he was shooting in. Also depending on the twist that was used in that rifle, had it gone subsonic, it likely will have pushed through it and reached a subsonic stability and continued its flight.

    Clear as mud right?
     

  3. eshell

    eshell Well-Known Member

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    VERY complicated subject for sure Meichele, with more variables than can be reckoned with for me to theorize.

    Below is a pic of my 24"x33" AR-500 steel plate, covered with bullet marks from 1,150 yards. The bullets that struck sideways are .308 168 grain Federal Gold Medal Match factory ammo, fired from a 26" PSS. They had still been hitting nose-on out to 1k, but fell apart not long after. Even sideways, at least some of them stayed relatively true to the aiming point. Everything else on the plate was still stable at that range and air density, and ranged from .243Win/115 DTACs to 6.5-284/Berger 140s, .300 WinMag Berger 210s and .308 175 FGMM factory ammo. IIRC, density altitude that day was around 2,500'.

    At Quantico MCB, VA, where altitude density is more often around 500 to 1000', the 168s will be often be sideways as close as 800 yards.

    [​IMG]
     
  4. britz

    britz Well-Known Member

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    One thing you have to keep in mind is that Hathcock shot a Viet chong solder at 2500 yards with a M2. It isn't proven that he got him in the first poke. ALso This wasn't the first time that Hathcock shot the m2 at range with his scope mounted on it. My point is that he could have easily sent several hundred rounds down range with the setup before actually making the hit at 2500 over the period of several months. He was shooting off of a fire base, not a sniper nest so he could have been (and most likely was) practicing for quite some time.

    Don't get me wrong, I know he was one of the best snipers the US has ever had, but you have to look at things the way they were.
     
  5. Mikecr

    Mikecr Well-Known Member

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    Yeah I'm gonna assume the whole sniper thing is pure BS..

    If you look at any drag curve, you'll see that drag peaks in the transonic region. It's lower subsonic. It's lower supersonic.
    Picking up & letting go of that shock wave is a huge, destabilizing change.
    It's been identified in much out of Aberdeen that any bullet's performance in this region is unpredictable. Normally seen as a disclaimer.
    It simply has to be tested to know, as with most anything aerodynamic.
     
  6. Michael Eichele

    Michael Eichele Well-Known Member

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    That sums it up VERY well.
     
  7. blackco

    blackco Well-Known Member

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    britz +1. In the back of one of Elmer Kieth's books he mentions that there is a lot of talk in the book about what he had shot with his pistols; it doesn't talk about how much he missed. If you shoot at something enough times eventually you will hit it. I meen this in no way to disparage Hathcock at all.

    Also, I don't know anything about it but I have heard the rimfire guys talk about keeping their bullets subsonic because of stability issues.
     
  8. mtmuley

    mtmuley Well-Known Member

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    I think even more impressive, is his hit on a Vietnamese General at 800(+or-) yards with his sniper issue Model 70 in 30-06. After, I believe, 8 days or so just getting THAT close. No walking that shot in. No spotter. No more General. mtmuley
     
  9. RBrowning

    RBrowning Well-Known Member

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    sonic transition

    I can't even carry the books written about aeronautics and ballastics, much less understand them. But I did see the darndest thing one day that relates to your question.

    Several of us had been shooting at a target at the other end of the field, 710 yards away. Our host said that he was going to shoot it with his 45-70 pistol. Being rather impressed at his abality with a 338 Yogi, I wasn't going to question his sanity, besides he had a loaded pistol and I didn't.

    He laid down and got ready. I got behind him with his Licea spotting scope to call his hit. He adjusted his scope and took the shot. Dirt flew up at about 450-500 yards down the field. He adjusted the scope and fired again. Same result. He adjusted up all the adjustment he had and still hit in about the same area. He held over on a tree in line with the target until he couldn't see the tree in the bottom of the scope. He still hit in the same area. Finally his wothless spotter decided to watch for the trace instead of just the point of impact. I couldn't believe my eyes when I watched his bullet get to about 400 yards and suddenly veer up and to the right then make a big clockwise circle until the bullet dug into the field at about 500 yards. When I told him what I saw he didn't believe it either. He took the spotting scope and had someone else shoot the pistol and he saw it happen too. Everytime it took the same path and hit in about the same spot, directly below where he was aiming. When he got home he ran his calculations again and sure enough the bullet would go sub-sonic at about 400 yards. Evidently the short stubby bullets responded very badly to the turbulence and went a bit wobbly.

    I decided that trying to get a bullet to go sub-sonic with any predicability may be a bit more of a challenge that I was up to. Good luck if you go there.
     
  10. sullijr

    sullijr Well-Known Member

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    BPCR silhouette shooters shoot 45/70's and hit very well past 400 yds,we have a Billy Dixon shoot and a buffalo at 1200 and 980 yds.The bullets are in the 400 gr region and reach the target or close to judging by the dirt flying consistantly.
     
  11. RBrowning

    RBrowning Well-Known Member

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    Isn't the BPCR for rifles? I don't think that a pistol will develop the velocity needed to maintain stability. But maybe I'm wrong, wouldn't be the first time. But I do know what I saw, and I saw it repeatedly. Then Eric saw it too. But it could be something else causing the bullet to go out of it's projected trajesctory at about the point where it went sub-sonic. I don't know for sure. Maybe that it being a pistol intended for normal ranges it had a slower twist and the bullet wasn't any too stable to begin with. Don't know.