Range Report Help With Drop table

[toddconley]

I know my drops for 100-700 at each 100 yards. I cannot find the correct data to get me in between them. 280 AI 180 gr Caurtusio Bullets. Dont know the exact bc. Somewhere between 650 and 7 is my best guess. Velocity is somewhere around 2800. Chrono not too accurate. HEre are the actual drops. Out to 500 no big deal to only have 100 data but after that the bullets are falling pretty fast.
Thanks,
T
325 4.25 moa
425 7.25
500 10.75
600 13.5
700 17.5
Can anybody help?

 

[BryanLitz]

Re: Help With Drop table

Todd,
On a quick glance, it looks like you're data suggests way more drop than is likely to be real.
Have you confirmed your sight calibration? In other words, when you dial the scope to 17.5 MOA, do you <span style="font-style: italic">know</span> if the scope is actually moving that much?
It's common to assume that a scopes adjustments are accurate, but that's not always the case. Shoot a group at 100 yards with your 100 yard zero, then moving the scope 20 MOA and shoot another group (you'll need a tall target). Measure the distance between the groups and see if it's what it should be.
This is also a good opportunity to make sure the scope is tracking vertically as well (draw a plumb line on the target and see if your POI shifts straight up).
Good luck,
-Bryan

 

[hue001t]

Re: Help With Drop table

cant you type into a program and have it increment for every 50 yards or on JBM i think you can type the specific yard lines you want drop for.

 

[toddconley]

Re: Help With Drop table

Brian,
You could very well be correct but I dont think so initialy. It is a nightforce nxs 5.5-22 and tracks repeatable at least up and and back to 0. I have two thing that are working against me. I dont know the accurate bc for the bullet and I think my chrono is not very good. I am shooting 55 gr rl 22 under a 189 caurterousio bullet. Quick load says that I should be getting 2660 but I think I am getting more than that. I am running a 28 in rock 5r tube. I also think that I am at the lower velocity node for this bullet and there is a higher velocity node to be found. Thoughts?

 

[BryanLitz]

Re: Help With Drop table

Todd,

I agree that the Nightforce scopes have very reliable adjustments, that's probably not your problem.

I was able to generate a trajectory that matches your data to within 0.15 MOA at all ranges except 500 yards using the following inputs:

G7 BC = .354 (this is a guess assuming a bullet profile similar to the Berger 180 VLD, and accounts for the extra 9 grains)
MV = 2600 fps
40 degrees F
Sea Level altitude (29.92 InHg)
0% RH
Sight height = 3 inches
Zero range = 100 yards

Data below is:
Range bullet path (inches)/MOA (error)
0 -3.00/NA
100 -0.00/0
325 -15.07/4.4 (+0.15)
425 -33.04/7.4 (+0.15)
500 -51.78/9.9 (-0.85)
600 -84.56/13.5 (0.00)
700 -127.23/17.4 (-0.10)

My guess is that quickload is probably correct about the low velocity. You may be getting even less than 2660 fps. I advise you shoot some rounds over a good chrono so you can gain confidence in your MV.

Good luck,
-Bryan

 

[toddconley]

Re: Help With Drop table

Wow, you might be worth that money for your book. Thanks for that. I have about 125 of these left that I am gonna shoot up, then I am going to 180 bergers so I can have some known numbers to work with. I am also going to go to RL 17 and ladder test them up to try to find a high velociy node to get the most out of this thing. But, not until after deer season. I shot some 1in groups yesterday in front of the local swat team at 500, 600, and 700 yds (no joke with witnesses) with this load. This thing is a hammer accuaracy wise and I am not going to change until after season. Thanks again for bring my confidence back up.