Is there a setting in JBM for 20 MOA bases?
Range Report JBM Calculator and 20 MOA bases
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Re: JBM Calculator and 20 MOA bases
No, a 20MOA canted base does not affect the JBM ballistics calculation.
No, a 20MOA canted base does not affect the JBM ballistics calculation.
Re: JBM Calculator and 20 MOA bases
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: One-Eyed Jack</div><div class="ubbcode-body">No, a 20MOA canted base does not affect the JBM ballistics calculation. </div></div>
Nore does the base effect the trajectory. The only conceivable point of interaction is the parameter that governs how high the scope is above the bore of the rifle.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: One-Eyed Jack</div><div class="ubbcode-body">No, a 20MOA canted base does not affect the JBM ballistics calculation. </div></div>
Nore does the base effect the trajectory. The only conceivable point of interaction is the parameter that governs how high the scope is above the bore of the rifle.
Re: JBM Calculator and 20 MOA bases
The reason you have a canted base (20 MOA) is to allow for more elevation from your zero. It does not effect the trajectory of the bullet.
The reason you have a canted base (20 MOA) is to allow for more elevation from your zero. It does not effect the trajectory of the bullet.
Re: JBM Calculator and 20 MOA bases
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sirk</div><div class="ubbcode-body">Is there a setting in JBM for 20 MOA bases? </div></div>
No, there isn't, but there is a drop-down menu for <span style="font-weight: bold"><span style="font-style: italic">"Cant Angle"</span></span> where you can input Cant Angle between -90.0 to 90.0 deg. The default is "0.0".
Why is the default "0.0"? Because there are 60 minutes to 1 degree, so a 20 MOA (20 Minute-Of-Angle) base would be about .33, or 1/3 of 1 MOA. I set the Cant Angle for .33 (Deg.) for my calculations for a 20 MOA base and the data I've gotten from the JBM program is usually right-on or RFC <span style="font-style: italic">(real fuckin' close)</span> for a couple of different .308s' with different specs. Obviously, info for each gun has to be tailored for each gun. However, I don't know if changing the default from "0.0" to ".33" has a significant, if any effect since I've never created and tested a data card using the default ("0.0").
The most important thing is to get accurate BC, muzzle velocity, and environmental data to input into JBM, along with the sight height for each gun you are making data cards for. You may have to tweek your cards a bit, but as long as you input accurate data JBM will get you close.
Keith
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sirk</div><div class="ubbcode-body">Is there a setting in JBM for 20 MOA bases? </div></div>
No, there isn't, but there is a drop-down menu for <span style="font-weight: bold"><span style="font-style: italic">"Cant Angle"</span></span> where you can input Cant Angle between -90.0 to 90.0 deg. The default is "0.0".
Why is the default "0.0"? Because there are 60 minutes to 1 degree, so a 20 MOA (20 Minute-Of-Angle) base would be about .33, or 1/3 of 1 MOA. I set the Cant Angle for .33 (Deg.) for my calculations for a 20 MOA base and the data I've gotten from the JBM program is usually right-on or RFC <span style="font-style: italic">(real fuckin' close)</span> for a couple of different .308s' with different specs. Obviously, info for each gun has to be tailored for each gun. However, I don't know if changing the default from "0.0" to ".33" has a significant, if any effect since I've never created and tested a data card using the default ("0.0").
The most important thing is to get accurate BC, muzzle velocity, and environmental data to input into JBM, along with the sight height for each gun you are making data cards for. You may have to tweek your cards a bit, but as long as you input accurate data JBM will get you close.
Keith
Re: JBM Calculator and 20 MOA bases
What you are looking for is the sight height setting... that is where the base comes into play.
Not the Cant.
You have to measure the center of the bore to the center of scope and adjust your sight height which is default at 1.5"
What you are looking for is the sight height setting... that is where the base comes into play.
Not the Cant.
You have to measure the center of the bore to the center of scope and adjust your sight height which is default at 1.5"
Re: JBM Calculator and 20 MOA bases
I use the JBM calculator frequently, and I have a 30 moa base on my 12 F/TR... assuming all the other parameters are entered accurately (temp, baro, etc.) it's usually very close to my actual come-ups. I've never even attempted to mess around with the angle mentioned above for this purpose. I'd worry more about getting accurate weather info and putting it in.
I use the JBM calculator frequently, and I have a 30 moa base on my 12 F/TR... assuming all the other parameters are entered accurately (temp, baro, etc.) it's usually very close to my actual come-ups. I've never even attempted to mess around with the angle mentioned above for this purpose. I'd worry more about getting accurate weather info and putting it in.
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