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Figuring Muzzle velocity

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  #8  
Unread 02-09-2009, 05:08 AM
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Re: Figuring Muzzle velocity

so perhaps I am going about this wrong. I am trying to refine my entries to dial in my POI and you folks are suggesting that I use my POI to refine my BC?
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  •   #9  
    Unread 02-09-2009, 08:03 AM
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    Re: Figuring Muzzle velocity

    Quote:
    Originally Posted by daveyj View Post
    so perhaps I am going about this wrong. I am trying to refine my entries to dial in my POI and you folks are suggesting that I use my POI to refine my BC?
    possibly. Published BC from some bullets are not exactly right. Your scope may not be moving .25" per hundred yards per click either.

    Make sure you are entering correct elevation and atmospheric conditions too.
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      #10  
    Unread 02-09-2009, 08:45 PM
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    Re: Figuring Muzzle velocity

    they wont match. actual data supercedes calculated data.
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      #11  
    Unread 02-09-2009, 09:39 PM
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    Re: Figuring Muzzle velocity

    Davey, see if this helps. Enter the data as accurately as possible into Exbal. Be as accurate as you can with this including all of the atmospheric data. Then, shoot a 3 shot group at a known distance, for me this was 675 yds. It's best if you shoot at a target or marked plate so you can identify and measure your POI. At this point, you want to measure your POI to see how low or high you were at this known range. Take the 3 shot average. Now, go back into Exbal and click Options, select Trajectory Validation. A box will open up with several small boxes inside it. You will be working off of the top row of three boxes. In the left box, enter the exact range you were shooting at, get this info from your laser rangefinder. In the box to the far right, enter either a + or - (for high or low) along with the exact measurement of how many inches low or high the average shot is for your group. For a 4 " high shot, this would look like this; +4. At this point, select calculate, then select apply. This will validate your drop sheet for this round. You will notice that it will automatically update all of your drop figures throughout the chart.
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      #12  
    Unread 02-10-2009, 09:43 PM
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    Re: Figuring Muzzle velocity

    I cant believe I havent done this before. I will give it a go and get back to you.
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      #13  
    Unread 02-10-2009, 10:16 PM
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    Re: Figuring Muzzle velocity

    Quote:
    Originally Posted by Moman View Post
    Davey, see if this helps. Enter the data as accurately as possible into Exbal. Be as accurate as you can with this including all of the atmospheric data. Then, shoot a 3 shot group at a known distance, for me this was 675 yds. It's best if you shoot at a target or marked plate so you can identify and measure your POI. At this point, you want to measure your POI to see how low or high you were at this known range. Take the 3 shot average. Now, go back into Exbal and click Options, select Trajectory Validation. A box will open up with several small boxes inside it. You will be working off of the top row of three boxes. In the left box, enter the exact range you were shooting at, get this info from your laser rangefinder. In the box to the far right, enter either a + or - (for high or low) along with the exact measurement of how many inches low or high the average shot is for your group. For a 4 " high shot, this would look like this; +4. At this point, select calculate, then select apply. This will validate your drop sheet for this round. You will notice that it will automatically update all of your drop figures throughout the chart.
    Yes it will correct the data, by adjusting the velocity. When I first chrongraphed my 338 Lapua with the 300 SMK I got a velocity of 2820 FPS. I found that I was quite low at 973 yards. The trajectory corrected the velocity and my drops were correct. But I didn't want to go that route at first so I adjusted the BC to .830 and that did not correct enough. I then decided to check my zero and I re-chronographed my load and this time I got a velocity of 2791 FPS average. Useing 2791 FPS my drops were and stil are right on. The trajectory validation had predicted 2790 FPS. I'll go that route from now on. Proper inof imput means proper info out put IMHO
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