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Help Needed with LB3.0 and .338 Bergers

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  #71  
Unread 06-09-2010, 04:30 AM
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Re: Help Needed with LB3.0 and .338 Bergers

MV = 2710
G7 BC = 0.419
DC = 0.870

Yields:
0.0 moa @ -> 300 yds
10.9 moa @->700yds
22.55 moa @ 1042yds
34.6 moa @->1342yds

That's the best I could do to model the trajectory provided in the initial Post, using the provided atmospheric conditions with coriolis and spin drift turned on. That MV is likely low, and the DC has been modified quite a bit which raises the red flag. This is a bit like a dog chasing its tail, and is why I prefer nailing down the MV. We're guessing on both the MV and the DC/BC in order to build a LB predicted trajectory to match the measured trajectory at these four yardages.

If I use the revised Berger G7 BC = 0.419 and a DC = 0.500, I can't closely match the drops/trajectory no matter which MV I use. The 1042 yd POI seems to require a higher BC than the 0.419 in order to match with the 700 and 1342yd POIs. The best MV match using a G7 BC = 0.419 and a DC = 0.500 is approximately 2742 fps.

Chronograph that puppy!
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  •   #72  
    Unread 06-09-2010, 05:01 AM
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    Re: Help Needed with LB3.0 and .338 Bergers

    Phorwarth,

    Did I miss some place the Latitude and Azimuth he was using?
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      #73  
    Unread 06-09-2010, 05:17 AM
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    Re: Help Needed with LB3.0 and .338 Bergers

    Eaglet,

    In Post #48, Broz stated "coriolis was 90* (east) and 46* lat" and I presumed those were applicable to the drop data from his first post.

    Last edited by phorwath; 06-09-2010 at 05:29 AM.
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      #74  
    Unread 06-09-2010, 05:37 AM
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    Re: Help Needed with LB3.0 and .338 Bergers

    Thanks!
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    -----------------------------
    HEBREWS 13:8
    Jesus Christ the same yesterday, and to day, and for ever.

    Our Lord Jesus said that as it was in the days of Noah and
    also as it was in the days of Lot so it shall be in the days...
    It's happening again!!! God sent to us His prophet, and His Word
    to this generation and we once more are rejecting it as was prophesied!!!

    ---> As promised, God Sent His Prophet to us!
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      #75  
    Unread 06-09-2010, 07:21 AM
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    Re: Help Needed with LB3.0 and .338 Bergers

    Quote:
    Originally Posted by phorwath View Post
    MV = 2710
    G7 BC = 0.419
    DC = 0.870

    Yields:
    0.0 moa @ -> 300 yds
    10.9 moa @->700yds
    22.55 moa @ 1042yds
    34.6 moa @->1342yds

    That's the best I could do to model the trajectory provided in the initial Post, using the provided atmospheric conditions with Coriolis and spin drift turned on. That MV is likely low, and the DC has been modified quite a bit which raises the red flag. This is a bit like a dog chasing its tail, and is why I prefer nailing down the MV. We're guessing on both the MV and the DC/BC in order to build a LB predicted trajectory to match the measured trajectory at these four yardages.

    If I use the revised Berger G7 BC = 0.419 and a DC = 0.500, I can't closely match the drops/trajectory no matter which MV I use. The 1042 yd POI seems to require a higher BC than the 0.419 in order to match with the 700 and 1342yd POIs. The best MV match using a G7 BC = 0.419 and a DC = 0.500 is approximately 2742 fps.

    Chronograph that puppy!
    Interesting, the DC is saying that something is not quite right with the BC... That brings me back to my guts feelings... Shawn Carlock did some shooting and never complained about the BC for them bullets to be off... you thought they were pretty much on, right? Well this is my thing:

    Coriolis and SD are ON
    SF = 1.63
    MV = 2705
    BC7 = 0.455
    DC = 0.500
    Running the application using the appropiate conditions and winds etc.
    this is what I get:

    300 yards -------0.0 ------
    700 yards -------1.5" high
    1042 yards -----2.2" low
    1342 yards -----0.0 -------

    With those results I'd be a happy camper!!!!!!!!!!!!!! I think your results up above, (Good job as a matter of fact) vindicates the results I get.
    When BC = 0.455 DC= is happy at 0.500 and look at the velocities... 2710 and 2705.... another thing, I understand that the EdGe is a bit faster than the LM... This is just an idea, 94 grains of H100 get you about 2825 with the EDGE
    I would guess 91.5 would bing it down to 2760 fps... with 30" barrel. The rifle in question has 27.5" which is about 2.5*25 = 62 fps less.... Then 2760 -62 = About 2700... Just me talking here; but would kind of make sense. Thats why
    I had said that before. Finally Using 0.455 is easy to make the curve match, using 0.419 it just won close.....

    When Broz gets tired and frustraded using the 0.419 BC7, he should go back to my above figures and he'll be a happy man!!!!!!!
    __________________
    -----------------------------

    -----------------------------
    HEBREWS 13:8
    Jesus Christ the same yesterday, and to day, and for ever.

    Our Lord Jesus said that as it was in the days of Noah and
    also as it was in the days of Lot so it shall be in the days...
    It's happening again!!! God sent to us His prophet, and His Word
    to this generation and we once more are rejecting it as was prophesied!!!

    ---> As promised, God Sent His Prophet to us!

    Last edited by Eaglet; 06-09-2010 at 07:42 AM.
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      #76  
    Unread 06-09-2010, 08:52 AM
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    Re: Help Needed with LB3.0 and .338 Bergers

    Not having a nailed down BC really screws up things, and not having a nailed down BC and MV is shooting in the dark it seems.
    Good thing is that the way that thing is shooting the bullets must be stable and not slumping. There seems to be a good case for using the original BC and the lower MV.
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      #77  
    Unread 06-09-2010, 09:52 AM
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    Re: Help Needed with LB3.0 and .338 Bergers

    Quote:
    Originally Posted by Eaglet View Post
    When Broz gets tired and frustraded using the 0.419 BC7, he should go back to my above figures and he'll be a happy man!!!!!!!
    You sound like you know me well.

    But here is my take, for what it is worth. I have been shooting this rifle for 3 years now and have close to 800 rounds through it. All this time have been with 300 smk's and I have chronoed it several times. Once on an oehler with a 92.5 gr load of H-1000. I can't remember exactly but I do remember it was lower than my chrono and I dont remember any red flag that day. I mean, if it only showed 2710 velocity I would have been alarmed and surprised. I think I remember 28 something which was par for the course on my exbal program.
    In short, I in no way feel that 2710 or less for velocity is accurate and I realize that I do need to get to an accurate chrono (oehler if possible) and see for sure.

    Yesterday alone I shot 4 distances all in the same direction. So if this azmuth and coriolis thing really brings something to the table we can use 90* east and lattitude of 46*.

    Here is the dope from yesterday.

    FC was all the same with the exception of temp I will note that with each shot.
    Baro for all was 25.75
    humidity 30

    700 yards temp 68 10.75 moa needed
    995 yards temp 59 20.00 moa needed
    1182 yards temp 65 27.25 moa needed
    1395 yards temp 61 36.00 moa used, one shot, 2" high

    Just for the sake of testing for the 1395 shot I left the windage at zero. It was dead calm both at the gun and target. These perfect conditions prompted me to gather data. With no wind, no spin drift added I hit dead center. Sure it was only one cold bore shot but I feel confident I could have shot two more and held 1/2 moa or very close.

    Guys, I am sorry, but I am slipping away here. The LB on my pda takes sooo long to give answers. I have to page back and forth to data tabs, wind tabs, drift tabs, environment tabs and shoot tabs. Some pages take 30 seconds or more to open. I feel this all is great for at home work but not for hunting and this concerns me.

    Late last night I loaded Bryans new G1 BC of .818 in my Nightforce exbal program. This with a velocity of 2795 gives me spot on elevation corrections for all the above listed distances and conditions I shot yesterday. Right down to the 1395 it calls for 35.75 moa.

    I am feeling that my time will be better spent learning my rifle and what it needs for windage to be effective at long distances. The simplicity ond the much faster results from Exbal keeps pulling me back.

    Like I said before, maybe my lack of computer skills and math is the problem and I need to accept that.

    The great news is I feel I have gained a very reliable and consistent load with the 300 gr Bergers. I am confident I can hold 1/2 moa groups at very long distances. That is worth a ton to me.

    Thanks!
    Jeff
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