Need some ballistics help...

[novaman64]

So have a new custom 280ai. Gunsmith worked up a load, and he was having fun with my rifle so took it out to 600, 800 and 1000 yards. That being said rifle is shooting Berger 168 VLD Hunting bullets, over 60.0 gr of H4831SC, and a mag primer (sight height of 1.75"). He said he chrono'd it at 3040, zero'd at 100 yards, and was shooting at 4800ft elevation, baro pressure was 24.8Hg. Anyways, he said at 600 yards drop was 9.5 moa, at 800 yards drop was 15.0 and at 1000 yards drop was 21.2 moa.

Plugged all the numbers into a few different ballistic apps (shooter and ballistic ae on my iphone) and the berger online ballistic app. Got data that matched his numbers...

Last weekend I went out to the range, temp was 67 deg, altitude was 245 ft, baro pressure was 29.894 Hg, plugged everything in, went out to 200 and shot 3 rounds. Calcs said should be 1.2 moa, dialed, and hit 1" high.
Went out to 300, calc said 3.0 moa, dialed it and hit 1.5 inches low.
400 yards calc said should be 5.2 moa, dialed it and hit 2.25 inches low.
And at 1000 yards said to dial 23.5 moa, shot that, and it had me 20 inches low.

Where am I going wrong?

 

[RockyMtnMT]

So have a new custom 280ai. Gunsmith worked up a load, and he was having fun with my rifle so took it out to 600, 800 and 1000 yards. That being said rifle is shooting Berger 168 VLD Hunting bullets, over 60.0 gr of H4831SC, and a mag primer (sight height of 1.75"). He said he chrono'd it at 3040, zero'd at 100 yards, and was shooting at 4800ft elevation, baro pressure was 24.8Hg. Anyways, he said at 600 yards drop was 9.5 moa, at 800 yards drop was 15.0 and at 1000 yards drop was 21.2 moa.

Plugged all the numbers into a few different ballistic apps (shooter and ballistic ae on my iphone) and the berger online ballistic app. Got data that matched his numbers...

Last weekend I went out to the range, temp was 67 deg, altitude was 245 ft, baro pressure was 29.894 Hg, plugged everything in, went out to 200 and shot 3 rounds. Calcs said should be 1.2 moa, dialed, and hit 1" high.
Went out to 300, calc said 3.0 moa, dialed it and hit 1.5 inches low.
400 yards calc said should be 5.2 moa, dialed it and hit 2.25 inches low.
And at 1000 yards said to dial 23.5 moa, shot that, and it had me 20 inches low.

Where am I going wrong?

Did you enter the dope for the zero? You may have to start over check your zero and muzzle vel.

Steve

 

[learning]

Not sure what optics you're using but a box test will give you a good idea if it's your scope not tracking?

 

[novaman64]

Did you enter the dope for the zero? You may have to start over check your zero and muzzle vel.

Steve

I did enter the dope for the zero...

 

[learning]

Also I think if you have a leopuld they used to be iphy and not moa like they said they were on the turret. I haven't looked at them in a while though

 

[novaman64]

Also I think if you have a leopuld they used to be iphy and not moa like they said they were on the turret. I haven't looked at them in a while though

Its the new VX6 3-18... I havent ran a box test but maybe I will.. Its the same scope my gunsmith used and he said it dialed up what his ballistic cal called for so I didnt think twice about it... If not, Ill have to grab a chrono and get back to the basics I guess....

 

[Jordan Smith]

Yup, chrono, check zero, and test the scope's adjustment increments.

 

[Bart B]

Having used several ballistic programs for a given bullet and muzzle velocity, all don't give the same results for the same environmental settings.

Boxing your scope shooting groups is not to precise. Instead, tape a ruler at right angles to your line of sight 50 or 100 yards away. Then clamp the rifle in a fixed position with the scope on that ruler. Zero the reticle on the ruler then move the reticule 10 major units; MOA, inches per hundred, mills or whatever. See where the reticle is on the ruler. Do the grade school math to calculate the error.

The muzzle velocity you get with that rifle and load is probably different than what the 'smith got. It's normal to see over 70 fps difference in average fps across several people shooting the same rifle and ammo. We all don't hold the rifle against our body with the same pressure; Newton's Law messes up the numbers across several people.

All scopes of a given make and model do not have exactly the same adjustment amount per click. All the lenses in each one don't have exactly the same focal length and that can cause a few percent spread in adjustment amount per click across all of them. It's caused by a small spread in target image size on the reticle plane for a given magnification set on the scope.