Would like verification form anyone experienced with JBM ballistic trajectory calculator. I just zeroed my AR15 at 25yds indoors. I want to adjust the elevation turret so that the rifle will be sighted at 100yds. According to JMB ballistic trajectory calculator when sighted at 25yds my 55gr bullets with a sight height of 2.8inches and traveling at 3000fps at the muzzle. will be 6.8inches high at 100yds. The calculator has a parameter called "zero height". Intuitively I know that the elevation turret must be lowered perhaps as much as 1 or 2 inches. So after several attempts I finally entered a negative 1.7inches in this space and recalculated which resulted in a 100yd zero. Did I use the JBM ballistic trajectory calculator correctly????
- Thread starter charliebrown1999
- Start date
Yes, 1.7” low at 25 sounds about right but that’s a roundabout way of doing it. Normally, just enter 100 yards as your zero and put range increment at 25. The calculator will show your required 25 yard point of impact for a 100 yard zero. With your sight height of 2.8 inches, the bullet rises to its max ord at around 110 (depending on your BC) then starts to fall.
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