How far have you adjusted BC on solvers to match real world hits?

[117D-RTO]

This week I was working up a new load using .264 Hornady 140gr BTHP, published G1 is .581. I got reliable hits out to around 700 yards but 800,900,and 1000 were well off the mark getting worse the farther I went out. I had to adjust BC in the Foretrex 701 w/AB to .518 to match real world hits, just wondering if this sounds way off the wall or if it's reasonable or doesn't matter as long as the math adds up.

For comparison using Hornady 4DOF I had to change Axial form factor to 1.06 to match up as well, not sure if that's a huge bump or not either. Monkey pressing buttons at this point, at least I have recorded DOPE eh?

 

[ma smith]

Does anyone have a reliable g7 on this bullet? I was using .285 (based off SH threads). G7 was just a hair off like .1 to .2 low at 600. 4DOF was spot on, however, so I am thinking the MV was correct and the drag models were different...Haven't had the range time to nail down better data so I'm all ears...


edited: double checked and it was starting at .285 as per post 3

 

[6.5SH]

A G7 of .285 is what I have recorded.

ETA:
This is with the 6.5 CM American Gunner @ 2669 fps.

JBM conversion to G1 gives .567 at that velocity.

 

[atepointer]

I have about 2,500 rounds of experience with the Hornady HPBT. The dope for me was accurate to 800 if I didn't use the 4dof that was awful in my hands. Endless axial tweaking no matter what that bullet was a nightmare with 4dof at any distance. When I plugged the G1 into regular BC calcs it was great from muzzle to 800. By 1000 it would get a bit low to the tune of about .2-.3. By 1200 that bullet was getting to be a 1.5moa goal. At 800 I'd make head shots on IPSC routinely and at 1,000 with a bit less confidence, but still a lot. At 1 mile I simply had to create a separate profile. Could get hits on a 3moa target, but pretty spotty and frustrating. For 800 and in that is one heck of a great pill and even further, but it didn't hold dope for me like a hamBerger Hybrid. That thing is hilarious out to 1 mile using G1 on any BC calc it's within .2 plus/minus every time. The true easy button. Also have a G7 profile for the Berger, but the G1 is more accurate for me so I stick with it.....from muzzle to mile. I don't ask why G1 is slightly better than G7 it just is.....I don't care why you call me just call...the consistency is there so I run with it.

I struggled with 4dof for about a year, but once I ditched it for G1 I was pulling hair less I just had a short dope and long dope. It wasn't a tweak thing for regular G1 I put in MV from chrono, listed G1 and went to work for both HPBT and Berger, but did find the HPBT to really start falling off by 1200.

 

[JAS-SH]

This week I was working up a new load using .264 Hornady 140gr BTHP, published G1 is .581. I got reliable hits out to around 700 yards but 800,900,and 1000 were well off the mark getting worse the farther I went out. I had to adjust BC in the Foretrex 701 w/AB to .518 to match real world hits, just wondering if this sounds way off the wall or if it's reasonable or doesn't matter as long as the math adds up.

For comparison using Hornady 4DOF I had to change Axial form factor to 1.06 to match up as well, not sure if that's a huge bump or not either. Monkey pressing buttons at this point, at least I have recorded DOPE eh?

1.06 is a small change. It that worked then 4DOF is working perfectly. The changes on POI at ranges upwards of 6-700 yards have more to do with other variables not directly related to BC. Hornady's 4DOF is not based on BC. It uses Drag vs. Mach number for calculations. 1.06 means you increased Drag (Cd) by ~5%.

In their extremely informative 4DOF Technical PDF they write "......the average vertical impact point at extended ranges is strongly influenced by things like the air density, average muzzle velocity, average projectile weight, as well as the average drag vs. Mach number profile."

I highly recommend reading their PDF, especially the part on the importance of having very accurate measurements of muzzle velocity and short range rifle zero. Small errors in those at 100 yard zeroes are greatly magnified at long ranges. Here's the link:

4DOF Technical Paper