HUGE BC change with opening up the hollow point.

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Michael Eichele, Oct 13, 2007.

  1. Michael Eichele

    Michael Eichele Well-Known Member

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    Just a small piece of info to file away if any of you decide to experiment with modifying the meplat of the SMK.

    I was out the last few days testing the 190 SMK's after having modified the meplat in an effort to get some reliable expansion on game and found that I had lost a huge amount of BC. It went from .574 to .451 in my rifle all else being equal. The meplat only grew by .005" but I opened the hollow point from .020" to .040". I was so shocked I decided to shoot more of the 100% factory bullets and they flew right where they should but the modified bullets always hit 15" lower (same POI at zero). I didnt think they would change that much but it is what it is.

    Regards.
     
  2. mikebob

    mikebob Well-Known Member

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    When that hipe came out I did some research on it and found an article from a benchrest shooter that came up with the same results as you, So i never got into it. In his article he stated he gained no accuracy either. I was wandering if you did or not
     

  3. Michael Eichele

    Michael Eichele Well-Known Member

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    I havent noticed any real accuracy changes to speak of. Most of the shooting I have been doing has been in a tough wind, so most of my groups have been a bit more open than normal at longer ranges. The times I have shot them at 300 yards with dead still air, I may have seen an ever so slight increase in accuracy but I wouldnt read into that too much with the minimal time I have been able to shoot in dead air at 300 yards.

    Bear in mind I didnt just uniform the meplats, I opened up the hollow point by 100%. I am sure this is where most of the BC loss is coming from.
     
  4. mikebob

    mikebob Well-Known Member

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    It was along time ago when i read that but I dont think his was that dramatic but same conclusion. I was trying to find it but cant remenber the name of the benchrest shooter it was. Are you going to try them on game to see if it expands better or are you going to drop it because of the bc loss. If it works better I might have to finally get mine out of the box.
     
  5. davewilson

    davewilson Well-Known Member

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    i'm getting ready to go shoot some 250SMK's that i've drilled the hollow point out to .047 i think it is. was hoping to do a bullet test at 1300, but we'll see how that goes. hopefully i'll get some come-ups and maybe a ballpark of BC.
     
  6. davewilson

    davewilson Well-Known Member

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    i wish i could tell you all about my shooting but when i went to leave this morning, i forgot to put the emergency brake on my truck and went back in the house to get something i forgot. of course the truck went rolling down a fairly big hill, across a normally wet area and bumped into the small stream where it's sitting now. needless to say i didn't go shooting.
     
  7. Len Backus

    Len Backus Administrator Staff Member

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    :(:(:(:(
     
  8. Shawn Carlock

    Shawn Carlock Sponsor

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    I discovered the same issue with the 300 gr SMK in the 338 Edge. I trimmed and opened the hollow point, more for expansion purposes than anything. At 1150 yards 1.50 moa lower same speed load etc. Like you shot some more unmodified bullets to the proper point of impact. I did not notice a improvement in vertical group size and could tell little difference in bullet performance so I bagged the extra work for more shooting time.
     
  9. philny1

    philny1 Well-Known Member

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    If I did that, I wouldn't tell anybody. No way!!
     
  10. davewilson

    davewilson Well-Known Member

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    i'm pretty sure it's totaled!
     
  11. Ronin

    Ronin Well-Known Member

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    Similar experience with 142 SMK at a 500 yard target the bullets were dropping 10" lower than expected.


    I wonder if there would be any merit in the idea of uniforming the meplat so all bullets are exactly equal in dimension and then running the bullets into a point forming die?

    What I'm getting at is uniform bullets with a meplat cut to 90 degree of bore,,, but still with a hollow point - (maybe- I know what I mean, but am too dumb to explain)

    The bullet would still expand - right?
     
  12. Mikecr

    Mikecr Well-Known Member

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    Interesting problem.
    Your BC should not have changed that much. People trim meplats all the time at around 2% loss in BC per .005" cut.

    Your describing a 21% loss without cutting, but opening the meplat .005" in diameter?
    Is this correct?
    Are you sure it isn't opening .05" in diameter?
     
  13. Michael Eichele

    Michael Eichele Well-Known Member

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    MikeCR, you are correct, but remember I also opend the hollow point by 100% from .020" too .040" That is most likely where most of my BC loss is coming from. The widened tip isnt much but the hole in the middle of it is doubled from factory.
     
  14. Mikecr

    Mikecr Well-Known Member

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    What lies WITHIN the meplat diameter doesn't affect supersonic BC.
    You could pack it full of material, or let it pack with air, the shockwave will bend the same around that point DIAMETER.

    So that diameter, the meplat, affects BC greatly. And boring out the hole, without increasing the meplat diameter, should affect nothing at all.