Trajectory of fmjbt .223

LarryB

May 14, 2002 14:10

I need info about the trajectory of an average .223 My understanding is that the bullet comes out of the barrell in a flat trajectory and then begins to drop as gravity and inertia take their toll. The trajectory charts that I've seen show the bullet talking a 'bell' pattern. Starting out low and arcing across a 'zero' line. Is the barrell of my ar15 angled up!? (wtf?)

Here's what I want to do: I have a ar15 scope with a bullet drop compensator knob. I shoot at a range at 25,50 100 and 200 yards. I'd like too be able to calibrate my scope so that I could adjust the bullet drop compensator so that I can zero in at 25, 50, 100 and 200 yards. Any suggetions

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  oneshy

  May 14, 2002 16:59

  Here's the way I understand it, and I'm open to correction. As the bullet leaves the barrel the velocity and spin on the projectile will cause the bullet to rise. Where the chart shows the bullet crossing the 0 line is "point blank" where the bullet and the line of sight from the barrel is the same. To set the BDC you can zero at say 100yd then there is usually a set screw or screws either on the side or top of the BDC knob that when removed or loosened ( depends on brand ) will allow the knob free movement. Some read 1, 2, 3 etc. these are 100yd. increments. Some will have marks between the no. if 5 marks, ea. would be 20yd. if 10 marks, 10 yd ea mark. You zero your rifle at 100yd set your loosened BDC at 0, tighten your set screws, then as you shoot at 200yd, turn your BDC to 1 then 300 is 2. If your BDC has smaller increments between the no. and you want to shoot at 25 or 50 yd, set your BDC to 1 at 100yd then turn back to 0 in increments corresponding to the yardage ea. increment. Do not use your BDC until you have your scope zeroed. I hope you have the instuctions on the method of loosening the BDC knob, as every brand seems to be a little different.
  
  Edited by - Oneshy on 05/14/2002 21:06:42

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  Tailgunner1954

  May 14, 2002 17:52

  OK basic balistics 101
  The bullet starts to drop due to gravity as soon as it leaves the barrel.
  The sight line and the bore line are NOT parallel, the barrel is tilted up slightly.
  The amount of tilt is determined by what range you want to zero for.
  The bullet crosses the sight line twice, once on the way up and again on the way back down (which is the range you normaly zero for)
  
  On your 223 with 1.5 in high sights and a 150 yard zero, you can expect the bullet to be 1-1/2 low at the muzzle, 5/8 low @25, 0 @50, 5/8 high @100, 0 @150, and 2 inchs low @200. Thats with out doing any adjustments to the sights.
  
  Edit to add: On a handgun the barrel is somtimes sloped down relative to the sights, but this is to compensate for the muzzel flip that occures before the bullet leaves the barrel.

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  Some guys like a mag full of lead, I still prefer one round to the head.
  
  Edited by - Tailgunner1954 on 05/14/2002 22:06:17

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