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2023 NH Silhouette Season  (last updated 6/23/2023 as results are collected from prior events)  Updated, no regional. April 30 PEMI LAR May ...

Thursday, June 16, 2011

JBM Trajectory web site. Free software on line.

When I first started this game some 10 years ago I was very analytical.  Now, I just go to the range and dial in my zeros.  Not sure why I changed my approach because the trajectory graph I used way back then was amazingly accurate.  Perhaps is it because I can get to a range easily and half the fun is shooting your equipment and finding your zeros.

In order to do my at home analysis I found this great free web software.  JBM software is very detailed but has great output.  The only guess work you have to do is to take a stab at your muzzle velocity.  Or, pull out the chronograph and get the real number for your favorite ammo and do it right.  I don't own a chronograph.

(This is a work in process post to see if I can get the data to stay with the link.)

Since we are heading to Hendrick Hudson in NY which uses yards and not meters it seemed like a good time to do some ballistics charts. Although there is a site in period it is nice to know what should happen to help sort through the chaos when getting sorted at a new range.

Here is a link to Aguila Match ammo so we know what the difference is between meters and yards.  From this data and knowing the following facts.

40y = 37m  so, instead of zero it is .3 moa higher or .25 moa for a scope.
60y = 55m  so, instead of 2.7 it is 2.0 moa or a difference of .7 or .75 for a scope
77y = 70m  so, instead of 5.6 it is 4.4 moa or a difference of 1.2 or 1.25 for a scope
100y = 91m so, instead of 9.7 it is 8.1 moa or a difference of 1.6 or 1.5 for a scope.

I used this chart to figure out what to expect at these distances against our current meter settings.  (Go to bottom and click on calculate) to get the raw data.  Or, use it for your gun.

The primary fly in the ointment is the assumption that the muzzle velocity out of my gun will be 1,050 FPS.  I don't own a chronograph and I guessed on the muzzle velocity.  I read it may be more like 1,025 FPS.

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