MinnMooney
Member
I have become a fanatic with the accuracy of turret adjustments and ballistic charts.
Let me explain : (0% - 22% correction factor w/various scopes)
Turret adj. accuracy -
Some (most) shooters assume that when they "dial in" 10 moa (or ") on their elevation turret that their bullet will hit 10 moa (or ") higher or lower at 100 yds. In the vast majority of scopes, this is just not the case. I go to great lengths with every new scope I buy to test and record the exact, actual adjustment value of it's 'clicks' as opposed to it's assumed value. I do this with the scope mounted or unmounted but always in an unmovable, clamped set-up. My surveyor's rod is 150' away and I take an initial reading with the turret all the way to the bottom (fully to the "Down" limit) and then take readings at every full rotation to the extreme "Up" limit. I know the extreme rod readings and the number of turret 'clicks' that I've turned. At that point it's easy to compare the two to get the "correction factor".
Example : Rod reading - 45" (90" @ 100 yds. OR 85.94 moa). Turret reading - 350 'clicks' @ 4 clicks per moa or ". Each 'click' = 24.56 moa or 25.714". So... I record on my cheat-sheet that if a range (ex. : 740 yds.) calls for 20 moa, I multiply the 20 by my correction factor 1.02 for moa (25/24.56). It calls for 20+1 click. Not much to worry about, right? But, what if the correction factor is 0.90 or - in the case of one of my semi-expensive ($550) scopes - 0.84 ?! In that extreme case, the turret adj would be 16+3 clicks. MAJOR difference at 740 yds. At 20 moa of turret, I would have hit at 23+3 moa or 29" high. Not even close for "1 shot - 1 kill".
This method (although time consuming at 1st) saves time and money in the long-run. It really shines when prairie dog shooting when I shoot hundreds of rounds a day and shoot 15-25 days per year.
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Ballistic chart accuracy -
I usually test my ballistic program in the field and adjust it accordingly. Here's how I do that :
I shoot 5-10 rounds at 100 yards through a chronograph for zero'ing and velocity. I then run a 'test' or preliminary ballistics chart using that bullet at that velocity. Five shots each at 200, 300 and 411 yds (my backyard range limit) are shot at gradually taller targets so I can hold at the top and measure actual drop from the 100 yard line-of-sight zero. I compare the acual drop at each yardage with the chart. If it isn't close enough for me then I "adjust" one or both of the factors that controls the arc like the ballistic coefficient (B.C.) or velocity (fps). In some cases, I have to adjust for multiple B.C.s at various velocities.
The end result is that I have a chart for that bullet, at that velocity & in those atmospheric conditions. The atmospheric data can be changed in a heartbeat after that with either a pocket PC or (in advance) a lap top with print-out.
WOW ! That took a while to write up.
I hope to get some comments back on my methods and if you are doing something similar.
Let me explain : (0% - 22% correction factor w/various scopes)
Turret adj. accuracy -
Some (most) shooters assume that when they "dial in" 10 moa (or ") on their elevation turret that their bullet will hit 10 moa (or ") higher or lower at 100 yds. In the vast majority of scopes, this is just not the case. I go to great lengths with every new scope I buy to test and record the exact, actual adjustment value of it's 'clicks' as opposed to it's assumed value. I do this with the scope mounted or unmounted but always in an unmovable, clamped set-up. My surveyor's rod is 150' away and I take an initial reading with the turret all the way to the bottom (fully to the "Down" limit) and then take readings at every full rotation to the extreme "Up" limit. I know the extreme rod readings and the number of turret 'clicks' that I've turned. At that point it's easy to compare the two to get the "correction factor".
Example : Rod reading - 45" (90" @ 100 yds. OR 85.94 moa). Turret reading - 350 'clicks' @ 4 clicks per moa or ". Each 'click' = 24.56 moa or 25.714". So... I record on my cheat-sheet that if a range (ex. : 740 yds.) calls for 20 moa, I multiply the 20 by my correction factor 1.02 for moa (25/24.56). It calls for 20+1 click. Not much to worry about, right? But, what if the correction factor is 0.90 or - in the case of one of my semi-expensive ($550) scopes - 0.84 ?! In that extreme case, the turret adj would be 16+3 clicks. MAJOR difference at 740 yds. At 20 moa of turret, I would have hit at 23+3 moa or 29" high. Not even close for "1 shot - 1 kill".
This method (although time consuming at 1st) saves time and money in the long-run. It really shines when prairie dog shooting when I shoot hundreds of rounds a day and shoot 15-25 days per year.
---------------------------------------------------------------------------
Ballistic chart accuracy -
I usually test my ballistic program in the field and adjust it accordingly. Here's how I do that :
I shoot 5-10 rounds at 100 yards through a chronograph for zero'ing and velocity. I then run a 'test' or preliminary ballistics chart using that bullet at that velocity. Five shots each at 200, 300 and 411 yds (my backyard range limit) are shot at gradually taller targets so I can hold at the top and measure actual drop from the 100 yard line-of-sight zero. I compare the acual drop at each yardage with the chart. If it isn't close enough for me then I "adjust" one or both of the factors that controls the arc like the ballistic coefficient (B.C.) or velocity (fps). In some cases, I have to adjust for multiple B.C.s at various velocities.
The end result is that I have a chart for that bullet, at that velocity & in those atmospheric conditions. The atmospheric data can be changed in a heartbeat after that with either a pocket PC or (in advance) a lap top with print-out.
WOW ! That took a while to write up.
I hope to get some comments back on my methods and if you are doing something similar.