Ballistics puzzler - 7.62x39 handloads

[Newtosavage]

I don't know why anybody would question modern ballistics calculators, they may not be perfect but they are pretty darn close as long as you enter accurate information. It's important to research bullet performance through ballistic calculators and other resources before choosing. It's a common revelation for people that start to do long range shooting that heavier bullets quite often (not always but most often) perform better at long range. For so many years people were taught that light/fast bullets were better but it's not necessarily true. You have to compare BC values, velocities, and environmental conditions in order to find what will work best and in the end test results are always the final word.

The only thing I'm questioning is the POI and why the 160's drop less than the 140's. According to the modern ballistic calculators, there should be a 0.1" difference. Not a 1.5" difference.

 

[jmr40]

Recoil has nothing to do with it- It's the bullet's weight.

Heavier bullets = more recoil. More recoil is causing the muzzle to rise more before the bullets exit the bore. The bullets better BC's could also be a contributor, but I don't think enough to make 1.5- 2" difference between 100 and 200 yards. The .1" difference calculated is probably about right if you discount muzzle rise. I've seen this happen before comparing 200 gr bullets to 180 gr bullets in 300 WSM. The 200's impact higher at 200-300 yards with both zeroed at 100. Beyond 300 yards the 180's have slightly less drop, but a lot less difference than you'd think.

Barrel harmonics play a part too. Most of the time when shooting bullets of similar weights you see predictable differences in bullet drop as range increases. It isn't unusual to see heavier bullets with more recoil and better BC's to come a lot closer to lighter bullets than many expect to see. But in rare cases I see differences of 2-3" in windage at 100 yards with certain bullets.

 

[Newtosavage]

At 100 yards, the only noticable difference in these bullets is windage. The 140's impact about 1/2" to the Left of the 160's.

 

[Llama Bob]

Heavier bullets = more recoil. More recoil is causing the muzzle to rise more before the bullets exit the bore. The bullets better BC's could also be a contributor, but I don't think enough to make 1.5- 2" difference between 100 and 200 yards. The .1" difference calculated is probably about right if you discount muzzle rise. I've seen this happen before comparing 200 gr bullets to 180 gr bullets in 300 WSM. The 200's impact higher at 200-300 yards with both zeroed at 100. Beyond 300 yards the 180's have slightly less drop, but a lot less difference than you'd think.

Barrel harmonics play a part too. Most of the time when shooting bullets of similar weights you see predictable differences in bullet drop as range increases. It isn't unusual to see heavier bullets with more recoil and better BC's to come a lot closer to lighter bullets than many expect to see. But in rare cases I see differences of 2-3" in windage at 100 yards with certain bullets.

All of this should be visible in the 100y zero.

 

[Haxby]

If this only happened once, it's just something that happened.
If it's repeatable, you can go to one of the good ballistic calculators, and plug in all the variables - sight height, altitude, atmospheric conditions, zero range, etc. - and find a pair of ballistic coefficients that match the actual trajectories.

 

[Newtosavage]

That's a good idea. I will try that.