5.56 Timeline

Ranges Notes

Had a Colt 6920 with a Trijicon TA31-MRD ACOG and a Spikes 5.45 with a TA31-ECOS ACOG side by side at the range today.  Both were zeroed using the 300m point of aim at 25 meters.  Later that day, both were used to shoot at a steel target at 565 yards(about 500 meters).  The Colt using M855 ammo and the ACOG calibrated for that ammo was right on for elevation when using the 500m mark.  However when shooting at 500m with the 5.45 and an identical 5.56 Bullet Drop Chart reticle, the 5.45 corresponded to the 400 meter mark on the BDC.

It was interesting to see how much flatter the 5.45 was flying compared to the same zero at the M4.  I’ve never been able to find good data on the ballistic coefficient of the 5.45 7n6 rounds, or readable info on its trajectory.

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0 thoughts on “Ranges Notes”

  1. I was shooting with the author that day. The 5.45 ammo was the 53 grain. I have sence checked the velocity online and it is distinctly slower than 5.56 55 grain. Not sure how the velocity compares to the 62 grain for which that scope is calibrated. The 53 grain 5.45 bullet is noticibly longer than the 55 grain 5.56, this makes me wonder if the bullets sectional density and ballistic coefficient were what made such a diference.


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