Subsonic bad?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by shaneman153d, Mar 18, 2010.

  1. shaneman153d

    shaneman153d Active Member

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    So what exactly happens to a bullet as it goes subsonic that makes it no good for shooting/hunting?

    I'm wondering because I just ordered me a nice .308 and I'm trying to figure out my max effective range for coyotes. It should still have the knockdown power beyond 1000yds, but I'm just wondering what else factors in?

    Looking at my ballistics program looks like it will stay supersonic (in this weather) to about 875-900.

    I almost can't wait to shoot out my 7mm so I can re-barrel that rig and get serious!

    Shane
     
  2. winmag

    winmag Well-Known Member

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    I belive most bullets become unstable when they go transonic. In other words instead of a ''spiral'' they fly more like a ''wounded duck'' just like a good throw vs a not so good throw with a football.(with alot less speed involved:D).
    Someone correct me if Im wrong. This is waht Ive been led to belive for years.
     

  3. Fitch

    Fitch Well-Known Member

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    What happens to the bullet as it transitions from supersonic through transonic to and then into subsonic flight depends on the bullet design. A rounded nose bullet that is short for it's weight will do just fine but it's performance in supersonic flight will be dissapointing because the BC won't be very good. A bullet with a long secant ogive and real high BC, (SMK and VLD for example), will not do as well in transonic and subsonic flight, but they will go a lot farther before they get into that speed range because of their high BC.

    My buddy has a .300 Whisper. He was having trouble with bullet stability shooting the heaviest SMK he could find - it was going sideways through the target at 100 yards. His timing was good - I'd just finished reading the chapter on stability in Litz's excellent book. Based on what I read in the book I suggested he go to the heaviest round nose bullet he could find. He did. It made nice round holes at 100 yards. Problem solved.

    A .308 is used a lot on paper at 1,000 yards - I don't see that cartridge as a 1,000 yard hunting round although it might work for coyotes.

    You mention a 7mmMAG. I havent' hunted with one ... yet. I just got one. Studying the ballistics for that cartridge has been interesting. It looks to me like it's a viable 1,000 yard cartridge for whitetail and smaller game with the right bullet. 7mm bullets have higher BC for their weight than .308 bullets. 7mm seems to a caliber where it "comes together" for long range shooting of high BC bullets out of a viable walk around hunting rifle with out a muzzle brake (a feature). Another one seems to be .338 but almost always with a muzzle brake unless the rifle weighs 20 lbs or more.

    Fitch
     
  4. tackb

    tackb Well-Known Member

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    I agree with fitch , i tried subsonic loads in my 308 and couldn't get match bullets to group so in desparation i tried some 180g flat base round nose over 7g of unique and voila instant inch groups at 100m ?
     
  5. shaneman153d

    shaneman153d Active Member

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    Interesting. So maybe the best thing to do (instead of relying on a ballistic calculator) would be to walk some paper out there and see when they start keyholing?

    I hear you on the 7mm. I've been shooting rocks out to 1000 with 162gr Amaxs. Next bullet I'm trying is going to be the Berger 180gr match hunting. BC is .659 and it's suitable for big game (Not that I'm to that level yet)
     
    Last edited: Mar 18, 2010
  6. Boss Hoss

    Boss Hoss Well-Known Member

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    Shooting at 300yards or less a FB is the best choice period. To make a very long story that would take too long to type----why do you think the BR guys such as myself use them exclusively and for my 1k rifle boat tails. This topic has been addressed numerous times so do a search on the topic and ye shall find the information that you seek.
     
  7. shaneman153d

    shaneman153d Active Member

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    Wrong thread?
     
  8. groper

    groper Well-Known Member

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    well, not all bullets are unstable as they go transonic, some are and some arnt... this has been proven many times. Read the jerry teo article shooting the .223 to a mile under MOA accuracy for more proof of this.

    The only thing that makes them bad for shooting/hunting, is whether they have enough energy and expansion for the desired animal your hunting. As for paper punching, well it dont matter at all, so long as they are accurate. But faster and higher BC is better for less wind dope error.
     
  9. topbrass

    topbrass Well-Known Member

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    Not centerfire, but .22lr is a good case. Standard Velocity and some High Velocity will go below supersonic within 100 yds. Yet there are very accurate rounds at 100 yds, particularly Standard Velocity.

    Look at the shape of a .22lr round. It has a round nose and is conical from the swagging to the base.
     
    Last edited: Mar 19, 2010
  10. Kevin Thomas

    Kevin Thomas Well-Known Member

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    Topbrass,

    A slight correction here; nearly all standard velocity 22 Long Rifle ammo is subsonic from the muzzle, and thereby avoids any transonic issues entirely. This is one of the reasons most standard velocity ammo tends to be more accurate than High Velocity fodder. This is also why you almost never see supersonic High Velocity ammo used in smallbore matches. Nasty things happen when a bullet goes transonic, but as has already been pointed out here, some bullets handle this better than others.

    Kevin Thomas
    Lapua USA
     
  11. topbrass

    topbrass Well-Known Member

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    I stand corrected.

    I guess there is no standard for standard velocity labeling since some are supersonic on their reported muzzle velocities, like Aguila SV 40gr RN at 1135 fps.

    Or maybe I dont know what the speed of sound is. 1125 fps at 68 degrees in dry air?
     
  12. 1300meters

    1300meters Well-Known Member

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    Here we go again. I don't think the bullet changes flight characteristics that much. But without the equipment to do the testing can't prove or disprove.but them boy's in afganaistan could probably could shed somelighton it.the 7pm rem mag works really well at 1000yds on game one elk @ 1024yds afew between 6@800 yds. It's about shot placement. Personal preference Berger bullets.goodshooting@good hunting 1300 meters
     
  13. topbrass

    topbrass Well-Known Member

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    Here we go again?

    This thread was dead two and a half years ago, before you found this place.
     
  14. 1300meters

    1300meters Well-Known Member

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    why ?