Fps and computer issue- advice please

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by BrentM, Sep 11, 2013.

  1. BrentM

    BrentM Well-Known Member

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    While up on the mountain this week I decided to shoot a rock at 1540 and was hoping for a first round hit. Nope high. Like 1 moa high.

    After several shots and misses I adjusted my speed and bingo. I ranged a new target at 1300 and bingo dead on.

    So the speed I have been using has been working at lower elevations seemingly fine.
    Meaning I have hit most targets with decent accuracy.

    Do you guys ever have to readjust speed or just use the computer? I am confused for sure. I am using shooter and needed to add 30 fps to the speed. I shot another 4 or 5 and they were good on elevation.
     
  2. Korhil78

    Korhil78 Well-Known Member

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    First question is are you using a weather station like a kestrel? If not then you will have to get the altitude from your gps to punch it in to shooter and get the baro, temp and other stuff from a local weather station on the Internet.

    If you are using a kestrel then you can set your kestrel altitude to 0 and get the station pressure from your kestrel and put that in shooter for your baro pressure. If you are doing it this way then you will need to go into shooter under the atmosphere section and turn "pressure is absolute" to ON. If you do it this way with a kestrel, you will never have to worry about what altitude you are at.

    Either way you do it..your dialing should not be off at all no matter what elevation you are at.
     

  3. Korhil78

    Korhil78 Well-Known Member

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    What I was sayig was hard to understand so I deleted it.
     
  4. BrentM

    BrentM Well-Known Member

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    I have a Kestrel 2500, Leica 1600, and a Garmin Rhino 655T. I use absolute baro and rarely use the GPS. The Leica gives me absolute so I tend to use it exclusively.

    I find it strange that my 6.5-284 appears to be shooting 3000 FPS at these elevations. I had to pull .5 MOA at 1000 to 1500 at a different location and now 1 moa at this location. Granted the further I shoot the more the MOA difference, I get that. I am just surprised. I am shooting the last of the same lot of bergers but I think this last lot of retumbo might be a bit faster, even though the lot number is the same.

    I am new to all this so seeing a speed increase of 30 fps seems strange given this rifle for the past 300 rounds has been dead on with 2970 as the shooter profile speed. I had not sent rounds at the higher elevations and struggle to see the correlation. The pressure at this site was 22.05 and 55 degrees.

    I am headed back up to this area this weekend to wolf hunt and want to send some more lead at that rock from the same spot. I was not impressed with my group at all at 1540. The wind was minimal but one round it was blowing the dust up the draw, the next round it was blowing it down the draw. At 1300 the bullet was 200 fps faster and deadly.

    Second question, is a 140 grain bullet at less than 1500 fps tumbling? My rifle is 1:8 twist.
     
  5. Max Heat

    Max Heat Well-Known Member

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    I don't claim to be an expert, but I'm pretty sure that the answer to question 2 is NO. This is based on the fact that bullets do not lose their spin nearly as quickly as they lose their velocity. In other words, it's spin should be much faster than that of a bullet just exiting the barrel at 1500fps.

    P.S. I forgot to mention that even if it DID have only half the spin at half the velocity, it likely would still be stable, because as velocity drops, the pressure point of it's drag friction moves farther to the rear, making it easier to stabilize. I once got reamed for failing to take this factor into account.
     
    Last edited: Sep 12, 2013
  6. BrentM

    BrentM Well-Known Member

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    Thanks. I called Berger and amazingly they answered immediately and the guy listened to me without laughing. It was felt the 140 pill would not destabilize until after 1200. 1400-1500 should still be producing good spin, as you suggested. I think my group issue has a lot more to do with ME and the wind shifts vs velocity and range.

    I will be up in the area and will plan to shoot again.
     
  7. Max Heat

    Max Heat Well-Known Member

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    I guess you didn't see that PS that I just added. But it's no biggie. Obviously the folks at berger know what they are talking about. I think wind would definitely be a huge factor at the distances you are shooting at. And VERY tricky to judge shot-to-shot, if it is mountainous terrain. Have fun, anyways!

    -Steve
     
  8. BrentM

    BrentM Well-Known Member

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    yes, mountains for sure. I was shooting from one mountain to other basically. So, from the face of one, across a big draw to the face of another. Wind at the shooter was weird and inconsistent, the bullet path put the bullet high across this draw and then down into the other face. At the face, the wind was weird there too. Swirling, up one shot, down the next, wind, then no wind.

    I am thinking across canyon/draw shooting is going to be what is the wind doing at my muzzle and forget the rest sort of deal. I am not sure how to determine what it is doing once you are past the trees and in this open air area. That bullet is traveling across 4500 feet of open air space.

    Yeah, wind is my problem and I am aware of it. It kicks my butt and I want to return the favor. : )
     
  9. Canadian Bushman

    Canadian Bushman Well-Known Member

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    From your situation i would def lean towards the possibility of an updraft.
    How much wind does it take to shift your bullet 1moa?

    Also how many bullet have you fired since your last cleaning? My rifle tends to pick up a little more speed after about 60 shots down the tube.

    I too use a leica 1600 and i like to let it sit out of its case in the open atmosphere for a while before i take a temp and pres. reading off of it because i notice i get a small deviation from when i first take it out to about 15 min later.

    Regardless id say repeat the shot on another day to verify.